diff --git a/doc/openstack-ops/ch_ops_network_troubleshooting.xml b/doc/openstack-ops/ch_ops_network_troubleshooting.xml index 63981716..9d5f4639 100644 --- a/doc/openstack-ops/ch_ops_network_troubleshooting.xml +++ b/doc/openstack-ops/ch_ops_network_troubleshooting.xml @@ -29,12 +29,12 @@ If you're encountering any sort of networking difficulty, one good initial sanity check is to make sure that your interfaces are up. For example: - $ ip a | grep state -1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN + $ ip a | grep state + 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br100 state UP qlen 1000 4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN -6: br100: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state +5: br100: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP You can safely ignore the state of virbr0, which is a default bridge created by libvirt and not used by @@ -44,32 +44,32 @@ UP Nova-Network Traffic in the Cloud If you are logged in to an instance and ping an external host, for example google.com, the ping packet takes the - following route: - + route: +
+ Traffic Route for Ping Packet - +
The instance generates a packet and places it on the virtual Network Interface Card (NIC) inside the instance, - such as, eth0. + such as eth0. The packet transfers to the virtual NIC of the compute host, such as, vnet1. You can find out - what vent NIC is being used by looking at the - /etc/libvirt/qemu/instance-xxxxxxxx.xml file. + what vnet NIC is being used by looking at the + /etc/libvirt/qemu/instance-xxxxxxxx.xml file. From the vnet NIC, the packet transfers to a - bridge on the compute node, such as, - br100. + bridge on the compute node, such as br100. If you run FlatDHCPManager, one bridge is on the compute node. If you run VlanManager, one @@ -80,7 +80,7 @@ UP Look for the vnet NIC. You can also reference nova.conf and look for the - flat_interface_bridge + flat_interface_bridge option. @@ -106,10 +106,10 @@ UP
OpenStack Networking Service Traffic in the Cloud - The OpenStack Networking Service, Neutron, has many more degrees - of freedom than nova-network does due to its pluggable back-end. It - can be configured with open source or vendor proprietary plugins - that control software defined networking (SDN) hardware or plugins + The OpenStack Networking Service, neutron, has many more degrees + of freedom than nova-network does because of its pluggable back end. It + can be configured with open source or vendor proprietary plug-ins + that control software defined networking (SDN) hardware or plug-ins that use Linux native facilities on your hosts such as Open vSwitch or Linux Bridge. The networking chapter of the OpenStack paths. The purpose of this section is to give you the tools to troubleshoot the various components involved however they are plumbed together in your environment. - For this example we will use the Open vSwitch (ovs) backend. Other back-end - plugins will have very different flow paths. OVS is the most + For this example we will use the Open vSwitch (OVS) back end. Other back-end + plug-ins will have very different flow paths. OVS is the most popularly deployed network driver according to the October - 2013 OpenStack User Survey with 50% more sites using it than + 2013 OpenStack User Survey, with 50 percent more sites using it than the second place Linux Bridge driver. We'll describe each step in turn with this diagram for reference: - +
+ Neutron Network Paths - +
The instance generates a packet and places it on - the virtual NIC inside the instance, such as, - eth0. + the virtual NIC inside the instance, such as eth0.
The packet transfers to a Test Access Point (TAP) device - on the compute host, such as, tap690466bc-92. You can find + on the compute host, such as tap690466bc-92. You can find out what TAP is being used by looking at the - /etc/libvirt/qemu/instance-xxxxxxxx.xml file. + /etc/libvirt/qemu/instance-xxxxxxxx.xml file.
The TAP device name is constructed using the first 11 - characters of the port id (10 hex digits plus an included + characters of the port ID (10 hex digits plus an included '-'), so another means of finding the device name is to use - the neutron command. This returns a pipe - delimited list, the first item of which is the port id. For - example to get the port id associated with IP address - 10.0.0.10: + the neutron command. This returns a pipe- + delimited list, the first item of which is the port ID. For + example, to get the port ID associated with IP address + 10.0.0.10, do this: # neutron port-list |grep 10.0.0.10|cut -d \| -f 2 ff387e54-9e54-442b-94a3-aa4481764f1d - Taking the first 11 characters we can construct a + Taking the first 11 characters, we can construct a device name of tapff387e54-9e from this output. The TAP device is connected to the integration bridge, br-int. This bridge connects all the instance TAP devices and any other bridges on the - system. In this example we have + system. In this example, we have int-br-eth1 and patch-tun. int-br-eth1 is one half of a veth pair connecting to the bridge - br-eth1 which handles VLAN networks + br-eth1, which handles VLAN networks trunked over the physical Ethernet device eth1. patch-tun is an Open - vSwitch internal port which connects to the + vSwitch internal port that connects to the br-tun bridge for GRE networks. The TAP devices and veth devices are normal Linux network devices and may be inspected with the usual tools such as ip and tcpdump. Open vSwitch internal - devices, such as patch-tun are only - visible within the Open vSwitch environment, if you - try to run tcpdump -i patch-tun it - will error saying the device does not exist. + devices, such as patch-tun, are only + visible within the Open vSwitch environment. If you + try to run tcpdump -i patch-tun, it + will raise an error saying that the device does not exist. It is possible to watch packets on internal interfaces, but it does take a little bit of - networking gymnastics. First we need to create a + networking gymnastics. First you need to create a dummy network device that normal Linux tools can see. - Then we need to add it to the bridge containing the - internal interface we want to snoop on. Finally we + Then you need to add it to the bridge containing the + internal interface you want to snoop on. Finally, you need to tell Open vSwitch to mirror all traffic to or from the internal port onto this dummy port. After all - this we can then run tcpdump on our + this, you can then run tcpdump on the dummy interface and see the traffic on the internal port. @@ -201,7 +201,7 @@ UP Create and bring up a dummy interface, - snooper0 + snooper0. # ip link add name snooper0 type dummy @@ -210,18 +210,19 @@ UP Add device snooper0 to bridge - br-int + br-int. # ovs-vsctl add-port br-int snooper0 Create mirror of patch-tun to - snooper0 (returns UUID of mirror port) + snooper0 (returns UUID of mirror port). # ovs-vsctl -- set Bridge br-int mirrors=@m -- --id=@snooper0 get Port snooper0 -- --id=@patch-tun get Port patch-tun -- --id=@m create Mirror name=mymirror select-dst-port=@patch-tun select-src-port=@patch-tun output-port=@snooper0 90eb8cb9-8441-4f6d-8f67-0ea037f40e6c - Profit. You can now see traffic on patch-tun by running tcpdump -i snooper0 + Profit. You can now see traffic on patch-tun by running + tcpdump -i snooper0. Clean up by clearing all mirrors on @@ -233,19 +234,23 @@ UP - On the integration bridge networks are + On the integration bridge, networks are distinguished using internal VLANs regardless of how the networking service defines them. This allows instances on the same host to communicate directly without transiting the rest of the virtual, or - physical, network. These internal VLAN id are based on + physical, network. These internal VLAN IDs are based on the order they are created on the node and may vary - between nodes. These ids are in no way related to the - segmentation ids used in the network definition and on + between nodes. These IDs are in no way related to the + segmentation IDs used in the network definition and on the physical wire. - VLAN tags are translated between the external tag, defined in the network settings, and internal tags in several places. On the br-int, incoming packets from the int-br-eth1 are translated from external tags to internal tags. Other translations also happen on the other bridges, and will be discussed in those sections. + VLAN tags are translated between the external tag, defined in the network + settings, and internal tags in several places. On the br-int, + incoming packets from the int-br-eth1 are translated from external + tags to internal tags. Other translations also happen on the other bridges and + will be discussed in those sections. - Discover which internal VLAN tag is in use for a + <title>To discover which internal VLAN tag is in use for a given external VLAN by using the <command>ovs-ofctl</command> command. @@ -270,10 +275,10 @@ UP # ovs-ofctl dump-flows br-int|grep vlan=2113 cookie=0x0, duration=173615.481s, table=0, n_packets=7676140, n_bytes=444818637, idle_age=0, hard_age=65534, priority=3,in_port=1,dl_vlan=2113 actions=mod_vlan_vid:7,NORMAL - Here we see packets received on port id 1 with the + Here you can see packets received on port ID 1 with the VLAN tag 2113 are modified to have the internal VLAN - tag 7. Digging a little deeper we can confirm that - port 1 is in face int-br-eth1. + tag 7. Digging a little deeper, you can confirm that + port 1 is in fact int-br-eth1. # ovs-ofctl show br-int OFPT_FEATURES_REPLY (xid=0x2): dpid:000022bc45e1914b n_tables:254, n_buffers:256 @@ -308,7 +313,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 GRE - VLAN based networks will exit the integration + VLAN-based networks exit the integration bridge via veth interface int-br-eth1 and arrive on the bridge br-eth1 on the other member of the veth pair @@ -322,19 +327,19 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 Packets, now tagged with the external VLAN tag, then exit onto the physical network via eth1. The Layer2 switch this interface is connected to must be - configured to accept traffic with the VLAN id used. + configured to accept traffic with the VLAN ID used. The next hop for this packet must also be on the - same Layer 2 network. + same layer-2 network. - GRE based networks are passed via + GRE-based networks are passed with patch-tun to the tunnel bridge br-tun on interface patch-int. This bridge also contains one port for each GRE tunnel peer, so one for each compute node and network node in your network. The ports are named sequentially from - gre-1 onwards. + gre-1 onward. Matching gre-<n> interfaces to tunnel endpoints is possible by looking at the Open vSwitch state: @@ -344,14 +349,14 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 type: gre options: {in_key=flow, local_ip="10.10.128.21", out_key=flow, remote_ip="10.10.128.16"} - In this case gre-1 is a tunnel from + In this case, gre-1 is a tunnel from IP 10.10.128.21, which should match a local interface on this node, to IP 10.10.128.16 on the remote side. These tunnels use the regular routing tables on the host to route the resulting GRE packet, so there is no requirement that GRE endpoints are all on the - same layer2 network, unlike VLAN + same layer-2 network, unlike VLAN encapsulation. All interfaces on the br-tun are internal to Open vSwitch. To monitor traffic on them @@ -361,16 +366,14 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 All translation of GRE tunnels to and from internal VLANs happens on this bridge. - Discover which internal VLAN tag is in use + <title>To discover which internal VLAN tag is in use for a GRE tunnel by using the <command>ovs-ofctl</command> command. - Find the - provider:segmentation_id of - the network you're interested in. This is - the same field used for VLAN id in VLAN - based networks + Find the provider:segmentation_id of the network + you're interested in. This is the same field used for the VLAN + ID in VLAN-based networks: # neutron net-show --fields provider:segmentation_id <network name> +--------------------------+-------+ | Field | Value | @@ -387,23 +390,23 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 ovs-ofctl dump-flows br-int: # ovs-ofctl dump-flows br-int|grep 0x3 - cookie=0x0, duration=380575.724s, table=2, n_packets=1800, n_bytes=286104, priority=1,tun_id=0x3 actions=mod_vlan_vid:1,resubmit(,10) +cookie=0x0, duration=380575.724s, table=2, n_packets=1800, n_bytes=286104, priority=1,tun_id=0x3 actions=mod_vlan_vid:1,resubmit(,10) cookie=0x0, duration=715.529s, table=20, n_packets=5, n_bytes=830, hard_timeout=300,priority=1,vlan_tci=0x0001/0x0fff,dl_dst=fa:16:3e:a6:48:24 actions=load:0->NXM_OF_VLAN_TCI[],load:0x3->NXM_NX_TUN_ID[],output:53 cookie=0x0, duration=193729.242s, table=21, n_packets=58761, n_bytes=2618498, dl_vlan=1 actions=strip_vlan,set_tunnel:0x3,output:4,output:58,output:56,output:11,output:12,output:47,output:13,output:48,output:49,output:44,output:43,output:45,output:46,output:30,output:31,output:29,output:28,output:26,output:27,output:24,output:25,output:32,output:19,output:21,output:59,output:60,output:57,output:6,output:5,output:20,output:18,output:17,output:16,output:15,output:14,output:7,output:9,output:8,output:53,output:10,output:3,output:2,output:38,output:37,output:39,output:40,output:34,output:23,output:36,output:35,output:22,output:42,output:41,output:54,output:52,output:51,output:50,output:55,output:33 - Here we see three flows related to this + Here, you see three flows related to this GRE tunnel. The first is the translation - from inbound packets with this tunnel id to - internal VLAN id 1. The second shows a + from inbound packets with this tunnel ID to + internal VLAN ID 1. The second shows a unicast flow to output port 53 for packets destined for MAC address fa:16:3e:a6:48:24. The third shows the translation from the internal VLAN representation to the GRE - tunnel id flooded to all output ports. For - further details of the flow descriptions see + tunnel ID flooded to all output ports. For + further details of the flow descriptions, see the man page for ovs-ofctl. As in the - VLAN example above, numeric port ids can be + VLAN example above, numeric port IDs can be matched with their named representations by examining the output of ovs-ofctl show br-tun. @@ -413,16 +416,14 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 - The packet is then received on the network node. Note that - any traffic to the l3-agent or dhcp-agent will only be - visible within their network namespace. Watching any - interfaces outside those namespaces, even those that carry - the network traffic will only show broadcast packets like - Address Resolution Protocols (ARPs), but unicast traffic to - the router or DHCP address will not be seen. See the section below for detail - on how to run commands within these namespaces. - Alternatively, it is possible to configure VLAN based + The packet is then received on the network node. Note that any traffic to the + l3-agent or dhcp-agent will be visible only within their network namespace. + Watching any interfaces outside those namespaces, even those that carry the + network traffic, will only show broadcast packets like Address Resolution + Protocols (ARPs), but unicast traffic to the router or DHCP address will not be + seen. See the section below for detail on + how to run commands within these namespaces. + Alternatively, it is possible to configure VLAN-based networks to use external routers rather than the l3-agent shown here, so long as the external router is on the same VLAN. @@ -430,19 +431,19 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 VLAN-based networks are received as tagged packets on a physical network interface, eth1 in - this example. Just as on the compute node this - interface is member of the br-eth1 + this example. Just as on the compute node, this + interface is a member of the br-eth1 bridge. - GRE based networks will be passed to the tunnel bridge - br-tun which behaves just like the + GRE-based networks will be passed to the tunnel bridge + br-tun, which behaves just like the GRE interfaces on the compute node. - Next the packets from either input go through the + Next, the packets from either input go through the integration bridge, again just as on the compute node. @@ -450,7 +451,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 The packet then makes it to the l3-agent. This is actually another TAP device within the router's network namespace. Router namespaces are named in the - form qrouter-<router-uuid> running + form qrouter-<router-uuid>. Running ip a within the namespace will show the TAP device name, qr-e6256f7d-31 in this example: @@ -463,7 +464,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 The qg-<n> interface in the l3-agent router namespace sends the packet on to its - next hop through device eth0 is on the + next hop through device eth0 on the external bridge br-ex. This bridge is constructed similarly to br-eth1 and may be inspected in the same way. @@ -476,8 +477,8 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 - DHCP-agents running on OpenStack networks run in - names spaces similar to the l3-agents. DHCP namespaces + DHCP agents running on OpenStack networks run in + namespaces similar to the l3-agents. DHCP namespaces are named qdhcp-<uuid> and have a TAP device on the integration bridge. Debugging of DHCP issues usually involves working inside this network @@ -488,7 +489,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0
Finding a Failure in the Path Use ping to quickly find where a failure exists in the - network path. In an instance, first see if you can ping an + network path. In an instance, first see whether you can ping an external host, such as google.com. If you can, then there shouldn't be a network problem at all. If you can't, try pinging the IP address of the compute @@ -499,7 +500,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 the problem is between the instance and the compute node. This includes the bridge connecting the compute node's main NIC with the vnet NIC of the instance. - One last test is to launch a second instance and see if + One last test is to launch a second instance and see whether the two instances can ping each other. If they can, the issue might be related to the firewall on the compute node. @@ -511,7 +512,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 tcpdump at several points along the network path to correlate where a problem might be. If you prefer working with a GUI, either live or by using a tcpdump - capture do also check out Wireshark (http://www.wireshark.org/). For example, run the following command: @@ -552,7 +553,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 12:51:42.020255 IP (tos 0x0, ttl 64, id 8137, offset 0, flags [none], proto ICMP (1), length 84) 1.2.3.4 > 203.0.113.30: ICMP echo reply, id 24895, seq 1, length 64 - On the Compute Node: + On the compute node: 12:51:42.019519 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84) 10.0.2.24 > 1.2.3.4: ICMP echo request, id 24895, seq 1, length 64 12:51:42.019519 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84) @@ -565,7 +566,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 1.2.3.4 > 10.0.2.24: ICMP echo reply, id 24895, seq 1, length 64 12:51:42.019807 IP (tos 0x0, ttl 61, id 8137, offset 0, flags [none], proto ICMP (1), length 84) 1.2.3.4 > 10.0.2.24: ICMP echo reply, id 24895, seq 1, length 64 - On the Instance: + On the instance: 12:51:42.020974 IP (tos 0x0, ttl 61, id 8137, offset 0, flags [none], proto ICMP (1), length 84) 1.2.3.4 > 10.0.2.24: ICMP echo reply, id 24895, seq 1, length 64 Here, the external server received the ping request and sent a @@ -590,7 +591,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 iptables.
- Network Configuration in the Database for nova-network + Network Configuration in the Database for Nova-Network With nova-network, the nova database table contains a few tables with networking information: @@ -612,46 +613,46 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 floating_ip. - From these tables, you can see that a Floating IP is + From these tables, you can see that a floating IP is technically never directly related to an instance, it must - always go through a Fixed IP. + always go through a fixed IP.
- Manually De-Associating a Floating IP - Sometimes an instance is terminated but the Floating + Manually Deassociating a Floating IP + Sometimes an instance is terminated but the floating IP was not correctly de-associated from that instance. Because the database is in an inconsistent state, the - usual tools to de-associate the IP no longer work. To + usual tools to deassociate the IP no longer work. To fix this, you must manually update the database. First, find the UUID of the instance in question: mysql> select uuid from instances where hostname = 'hostname'; - Next, find the Fixed IP entry for that UUID: + Next, find the fixed IP entry for that UUID: mysql> select * from fixed_ips where instance_uuid = '<uuid>'; - You can now get the related Floating IP + You can now get the related floating IP entry: mysql> select * from floating_ips where fixed_ip_id = '<fixed_ip_id>'; - And finally, you can de-associate the Floating + And finally, you can deassociate the floating IP: mysql> update floating_ips set fixed_ip_id = NULL, host = NULL where fixed_ip_id = '<fixed_ip_id>'; - You can optionally also de-allocate the IP from the + You can optionally also deallocate the IP from the user's pool: mysql> update floating_ips set project_id = NULL where fixed_ip_id = '<fixed_ip_id>';
- Debugging DHCP Issues with nova-network + Debugging DHCP Issues with Nova-Network One common networking problem is that an instance boots successfully but is not reachable because it failed to obtain an IP address from dnsmasq, which is the DHCP server that is launched by the nova-network service. - The simplest way to identify that this the problem with + The simplest way to identify that this is the problem with your instance is to look at the console output of your instance. If DHCP failed, you can retrieve the console log by doing: @@ -659,7 +660,7 @@ OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0 If your instance failed to obtain an IP through DHCP, some messages should appear in the console. For example, for the Cirros image, you see output that looks - like: + like the following: udhcpc (v1.17.2) started Sending discover... Sending discover... @@ -682,7 +683,7 @@ unreachable root: # killall dnsmasq # restart nova-network - It's openstack-nova-network on RHEL/CentOS/Fedora but nova-network on Ubuntu/Debian. + Use openstack-nova-network on RHEL/CentOS/Fedora but nova-network on Ubuntu/Debian. Several minutes after nova-network is restarted, you should see new dnsmasq processes running: # ps aux | grep dnsmasq @@ -696,13 +697,13 @@ root 3736 0.0 0.0 27512 444 ? S 15:40 0:00 /usr/sbin/dnsmasq --strict-order --bi --dhcp-hostsfile=/var/lib/nova/networks/nova-br100.conf --dhcp-script=/usr/bin/nova-dhcpbridge --leasefile-ro If your instances are still not able to obtain IP - addresses, the next thing to check is if dnsmasq is seeing + addresses, the next thing to check is whether dnsmasq is seeing the DHCP requests from the instance. On the machine that is running the dnsmasq process, which is the compute host if running in multi-host mode, look at /var/log/syslog to see the dnsmasq output. If dnsmasq is seeing the request properly and handing out an IP, the output looks - like: + like this: Feb 27 22:01:36 mynode dnsmasq-dhcp[2438]: DHCPDISCOVER(br100) fa:16:3e:56:0b:6f Feb 27 22:01:36 mynode dnsmasq-dhcp[2438]: DHCPOFFER(br100) 192.168.100.3 fa:16:3e:56:0b:6f Feb 27 22:01:36 mynode dnsmasq-dhcp[2438]: DHCPREQUEST(br100) 192.168.100.3 fa:16:3e:56:0b:6f @@ -710,24 +711,24 @@ Feb 27 22:01:36 mynode dnsmasq-dhcp[2438]: DHCPACK(br100) 192.168.100.3 fa:16:3e:56:0b:6f test If you do not see the DHCPDISCOVER, a problem exists with the packet getting from the instance to the machine - running dnsmasq. If you see all of above output and your - instances are still not able to obtain IP addresses then + running dnsmasq. If you see all of the preceding output and your + instances are still not able to obtain IP addresses, then the packet is able to get from the instance to the host running dnsmasq, but it is not able to make the return trip. - If you see any other message, such as: + You might also see a message such as this: Feb 27 22:01:36 mynode dnsmasq-dhcp[25435]: DHCPDISCOVER(br100) fa:16:3e:78:44:84 no address available - Then this may be a dnsmasq and/or nova-network related + This may be a dnsmasq and/or nova-network related issue. (For the example above, the problem happened to be that dnsmasq did not have any more IP addresses to give - away because there were no more Fixed IPs available in the + away because there were no more fixed IPs available in the OpenStack Compute database). If there's a suspicious-looking dnsmasq log message, take a look at the command-line arguments to the dnsmasq processes to see if they look correct. $ ps aux | grep dnsmasq - The output looks something like: + The output looks something like the following: 108 1695 0.0 0.0 25972 1000 ? S Feb26 0:00 /usr/sbin/dnsmasq -u libvirt-dnsmasq --strict-order --bind-interfaces --pid-file=/var/run/libvirt/network/default.pid --conf-file= --except-interface lo --listen-address 192.168.122.1 --dhcp-range 192.168.122.2,192.168.122.254 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases @@ -745,84 +746,84 @@ nobody 2438 0.0 0.0 27540 1096 ? S Feb26 0:00 /usr/sbin/dnsmasq --strict-order - dnsmasq process that has the DHCP subnet range of 192.168.122.0 belongs to libvirt and can be ignored. The other two dnsmasq processes belong to nova-network. The - two processes are actually related -- one is simply the + two processes are actually related—one is simply the parent process of the other. The arguments of the dnsmasq processes should correspond to the details you configured nova-network with. If the problem does not seem to be related to dnsmasq - itself, at this point, use tcpdump on the interfaces to + itself, at this point use tcpdump on the interfaces to determine where the packets are getting lost. DHCP traffic uses UDP. The client sends from port 68 to port 67 on the server. Try to boot a new instance and then systematically listen on the NICs until you identify the - one that isn't seeing the traffic. To use tcpdump to + one that isn't seeing the traffic. To use tcpdump to listen to ports 67 and 68 on br100, you would do: # tcpdump -i br100 -n port 67 or port 68 You should be doing sanity checks on the interfaces - using command such as "ip a" and "brctl - show" to ensure that the interfaces are + using command such as ip a and brctl + show to ensure that the interfaces are actually up and configured the way that you think that they are.
Debugging DNS Issues - If you are able to ssh into an instance, but it takes a + If you are able to use SSH to log into an instance, but it takes a very long time (on the order of a minute) to get a prompt, then you might have a DNS issue. The reason a DNS issue - can cause this problem is that the ssh server does a + can cause this problem is that the SSH server does a reverse DNS lookup on the IP address that you are connecting from. If DNS lookup isn't working on your instances, then you must wait for the DNS reverse lookup - timeout to occur for the ssh login process to + timeout to occur for the SSH login process to complete. - When debugging DNS issues, start by making sure the host + When debugging DNS issues, start by making sure that the host where the dnsmasq process for that instance runs is able to correctly resolve. If the host cannot resolve, then the - instances won't be able either. - A quick way to check if DNS is working is to - resolve a hostname inside your instance using the + instances won't be able to either. + A quick way to check whether DNS is working is to + resolve a hostname inside your instance by using the host command. If DNS is working, you should see: - $ host openstack.org -openstack.org has address 174.143.194.225 + $ host openstack.org +openstack.org has address 174.143.194.225 openstack.org mail is handled by 10 mx1.emailsrvr.com. -openstack.org mail is handled by 20 mx2.emailsrvr.com. +openstack.org mail is handled by 20 mx2.emailsrvr.com. If you're running the Cirros image, it doesn't have the "host" program installed, in which case you can use ping - to try to access a machine by hostname to see if it + to try to access a machine by hostname to see whether it resolves. If DNS is working, the first line of ping would be: - $ ping openstack.org -PING openstack.org (174.143.194.225): 56 data bytes + $ ping openstack.org +PING openstack.org (174.143.194.225): 56 data bytes If the instance fails to resolve the hostname, you have a DNS problem. For example: - $ ping openstack.org -ping: bad address 'openstack.org' + $ ping openstack.org + ping: bad address 'openstack.org' In an OpenStack cloud, the dnsmasq process acts as the DNS server for the instances in addition to acting as the DHCP server. A misbehaving dnsmasq process may be the source of DNS-related issues inside the instance. As mentioned in the previous section, the simplest way to - rule out a misbehaving dnsmasq process is to kill all of - the dnsmasq processes on the machine, and restart + rule out a misbehaving dnsmasq process is to kill all + the dnsmasq processes on the machine and restart nova-network. However, be aware that this command affects everyone running instances on this node, including tenants that have not seen the issue. As a last resort, as root: # killall dnsmasq # restart nova-network - After the dnsmasq processes start again, check if DNS is + After the dnsmasq processes start again, check whether DNS is working. If restarting the dnsmasq process doesn't fix the issue, you might need to use tcpdump to look at the packets to trace where the failure is. The DNS server listens on UDP port 53. You should see the DNS request on the bridge - (such as, br100) of your compute node. If you start + (such as, br100) of your compute node. Let's say you start listening with tcpdump on the compute node: # tcpdump -i br100 -n -v udp port 53 tcpdump: listening on br100, link-type EN10MB (Ethernet), capture size 65535 bytes - Then, if you ssh into your instance and try to + Then, if you use SSH to log into your instance and try ping openstack.org, you should see something like: 16:36:18.807518 IP (tos 0x0, ttl 64, id 56057, offset 0, flags [DF], proto UDP (17), length 59) @@ -833,10 +834,10 @@ bytes
Troubleshooting Open vSwitch - Open vSwitch as used in the OpenStack Networking Service examples - above is full-featured multilayer virtual switch licensed under the + Open vSwitch as used in the previous OpenStack Networking Service examples + is a full-featured multilayer virtual switch licensed under the open source Apache 2.0 license. Full documentation can be found at - the project's web site http://openvswitch.org/. In practice, given the configuration above, the most common issues are being sure that the required bridges (br-int, br-tun, @@ -845,13 +846,13 @@ bytes The Open vSwitch driver should and usually does manage this automatically, but it is useful to know how to do this by hand with the ovs-vsctl command. - This command has many more sub commands that we will use here see the man - page or ovs-vsctl --help for the full + This command has many more subcommands than we will use here; see the man + page or use ovs-vsctl --help for the full listing. To list the bridges on a system use ovs-vsctl - list-br. This example shows a compute node which has - internal bridge and tunnel bridge. VLAN networks are trunked + list-br. This example shows a compute node that has an + internal bridge and a tunnel bridge. VLAN networks are trunked through the eth1 network interface: # ovs-vsctl list-br @@ -861,8 +862,8 @@ eth1-br Working from the physical interface inwards, we can see the - chain of ports and bridges. First the bridge - eth1-br which contains the physical network + chain of ports and bridges. First, the bridge + eth1-br, which contains the physical network interface eth1 and the virtual interface phy-eth1-br. @@ -871,10 +872,10 @@ eth1-br phy-eth1-br - Next the internal bridge, br-int, contains - int-eth1-br which pairs with the - phy-eth1-br to connect to the physical network we - saw in the previous bridge, br-tun, which is used + Next, the internal bridge, br-int, contains + int-eth1-br, which pairs with + phy-eth1-br to connect to the physical network shown + in the previous bridge, br-tun, which is used to connect to the GRE tunnel bridge and the TAP devices that connect to the instances currently running on the system. @@ -888,7 +889,7 @@ tap8a864970-2d The tunnel bridge, br-tun, contains the patch-int interface and - gre-<N> interfaces for each peer in + gre-<N> interfaces for each peer it connects to via GRE, one for each compute and network node in your cluster. @@ -905,20 +906,20 @@ gre-<N> ovs-vsctl add-br and ports can be added to bridges with ovs-vsctl add-port. While running these by hand can be useful debugging, it is imperative - that manual changes which you intend to keep be reflected back + that manual changes that you intend to keep be reflected back into your configuration files.
- Dealing with network namespaces + Dealing with Network Namespaces Linux network namespaces are a kernel feature the - networking service uses to support multiple isolated layer2 + networking service uses to support multiple isolated layer-2 networks with overlapping IP address ranges. The support may be - disabled, but is on by default. If it is enabled in your + disabled, but it is on by default. If it is enabled in your environment, your network nodes will run their dhcp-agents and l3-agents in isolated namespaces. Network interfaces and traffic on those interfaces will not be visible in the default namespace. - To see if you are using namespaces run ip netns + To see whether you are using namespaces, run ip netns # ip netns qdhcp-e521f9d0-a1bd-4ff4-bc81-78a60dd88fe5 @@ -934,10 +935,10 @@ qrouter-8a4ce760-ab55-4f2f-8ec5-a2e858ce0d39 and their UUIDs can be obtained buy running neutron net-list with administrative credentials. Once you've determined which namespace you need to work in, - you can use any of the debugging tools mention above by prefixing + you can use any of the debugging tools mention earlier by prefixing the command with ip netns exec <namespace>. For example, to see what network interfaces - exist in the first qdhcp name space returned above: + exist in the first qdhcp namespace returned above, do this: # ip netns exec qdhcp-e521f9d0-a1bd-4ff4-bc81-78a60dd88fe5 ip a 10: tape6256f7d-31: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN link/ether fa:16:3e:aa:f7:a1 brd ff:ff:ff:ff:ff:ff @@ -951,15 +952,15 @@ qrouter-8a4ce760-ab55-4f2f-8ec5-a2e858ce0d39 inet6 ::1/128 scope host valid_lft forever preferred_lft forever - From this we see that the DHCP server on that network is + From this you see that the DHCP server on that network is using the tape6256f7d-31 device and has an IP address - 10.0.1.100, seeing the address 169.254.169.254 we can also see + 10.0.1.100. Seeing the address 169.254.169.254, you can also see that the dhcp-agent is running a metadata-proxy service. Any of the commands mentioned previously in this chapter can be run in the same way. It is also possible to run a shell, such as bash, and have an interactive session within - the namespace. In the latter case exiting the shell will return - you to the top level default namespace. + the namespace. In the latter case, exiting the shell returns + you to the top-level default namespace.
Summary