Stephen Hemminger
2017-Dec-15 15:55 UTC
[Bridge] linux bridge does not forward arp reply back packets in a vmware vm
On Fri, 15 Dec 2017 15:37:39 +0200 Adrian P <adrian27oradea at gmail.com> wrote:> Hello, > > I have a strange issue with a linux bridge created by > openstack-neutron (pike release). This linux bridge is hosted in a > vmware VM running latest CentOS 7, with a single network interface in > promiscuous mode. > > From openstack neutron perspective, the networking setup is simple: a > single flat external provider network, with a single cirros VM > instance connected to it. > > Therefore, in the linux bridge running in the vmware host, I have 3 interfaces: > > # brctl show > bridge name bridge id STP enabled interfaces > brq025a9a94-58 8000.005056a6b378 no ens160 > tap2eb4cad6-cd > <----- neutron DHCP agent tap interface > tap6d31a191-9f > <----- cirros VM instance tap interface > > The ens160 is the "physical" CentOS 7 host interface, that is in > promiscuous mode. > > The tap2eb4cad6-cd tap interface is the neutron DHCP agent interface, > and the tap6d31a191-9f tap interface is used by the cirros VM > instance. > > The problem is the following: > > With a tcpdump, I am able to see the arp request (ARP, Request who-has > 10.20.21.1 tell 10.20.21.233) going out from the cirros VM instance on > tap interface tap6d31a191-9f, and well as on the bridge itself > (brq025a9a94-58). However, the reply back to the arp request (Reply > 10.20.21.1 is-at 00:17:08:c4:52:80) does not reach the cirros VM > instance anymore. With tcpdump, I am able to see the arp reply back > packets in the bridge (brq025a9a94-58), however they do not show up > anymore on the cirros VM instance tap interface tap6d31a191-9f. > > To me it seems that for whatever reason, the bridge does not forward > the arp reply back packets to the cirros VM tap interface, and I do > not understand why. The strange thing is that after a while, for > apparently no reason, a single arp reply back packet gets through the > bridge and the tap interface, and the arp table gets updated with > correct IP address in the cirros VM instance. However, if I clean up > the arp table in the cirros VM instance, it takes again 10 to 15 > minutes of continuously sending arp requests, until a single arp reply > back packets gets through. > > I was banging my head to the table for a few days with this issue, and > finally, for apparent no reason, I manually configured the bridge max > aging time to 0, to convert it in a hub, and from that moment > everything started to work without any issue. Still, I do no > understand why is this happening, and obviously I cannot manually set > up the bridge aging time to 0 all the time in all the bridges > openstack neutron creates automatically. > > Any thoughts? > > Many thanks in advance. > > Best regards, > AdrianDoes each tap instance and the ens160 have a different and valid Ethernet address? Also make sure the these are in the bridge forwarding table.
Adrian P
2017-Dec-15 16:29 UTC
[Bridge] linux bridge does not forward arp reply back packets in a vmware vm
On Fri, Dec 15, 2017 at 5:55 PM, Stephen Hemminger <stephen at networkplumber.org> wrote:> On Fri, 15 Dec 2017 15:37:39 +0200 > Adrian P <adrian27oradea at gmail.com> wrote: > >> Hello, >> >> I have a strange issue with a linux bridge created by >> openstack-neutron (pike release). This linux bridge is hosted in a >> vmware VM running latest CentOS 7, with a single network interface in >> promiscuous mode. >> >> From openstack neutron perspective, the networking setup is simple: a >> single flat external provider network, with a single cirros VM >> instance connected to it. >> >> Therefore, in the linux bridge running in the vmware host, I have 3 interfaces: >> >> # brctl show >> bridge name bridge id STP enabled interfaces >> brq025a9a94-58 8000.005056a6b378 no ens160 >> tap2eb4cad6-cd >> <----- neutron DHCP agent tap interface >> tap6d31a191-9f >> <----- cirros VM instance tap interface >> >> The ens160 is the "physical" CentOS 7 host interface, that is in >> promiscuous mode. >> >> The tap2eb4cad6-cd tap interface is the neutron DHCP agent interface, >> and the tap6d31a191-9f tap interface is used by the cirros VM >> instance. >> >> The problem is the following: >> >> With a tcpdump, I am able to see the arp request (ARP, Request who-has >> 10.20.21.1 tell 10.20.21.233) going out from the cirros VM instance on >> tap interface tap6d31a191-9f, and well as on the bridge itself >> (brq025a9a94-58). However, the reply back to the arp request (Reply >> 10.20.21.1 is-at 00:17:08:c4:52:80) does not reach the cirros VM >> instance anymore. With tcpdump, I am able to see the arp reply back >> packets in the bridge (brq025a9a94-58), however they do not show up >> anymore on the cirros VM instance tap interface tap6d31a191-9f. >> >> To me it seems that for whatever reason, the bridge does not forward >> the arp reply back packets to the cirros VM tap interface, and I do >> not understand why. The strange thing is that after a while, for >> apparently no reason, a single arp reply back packet gets through the >> bridge and the tap interface, and the arp table gets updated with >> correct IP address in the cirros VM instance. However, if I clean up >> the arp table in the cirros VM instance, it takes again 10 to 15 >> minutes of continuously sending arp requests, until a single arp reply >> back packets gets through. >> >> I was banging my head to the table for a few days with this issue, and >> finally, for apparent no reason, I manually configured the bridge max >> aging time to 0, to convert it in a hub, and from that moment >> everything started to work without any issue. Still, I do no >> understand why is this happening, and obviously I cannot manually set >> up the bridge aging time to 0 all the time in all the bridges >> openstack neutron creates automatically. >> >> Any thoughts? >> >> Many thanks in advance. >> >> Best regards, >> Adrian > > Does each tap instance and the ens160 have a different and valid Ethernet > address? Also make sure the these are in the bridge forwarding table.Yes, they have valid Ethernet addresses, and they do show up in the forwarding table twice, see below: # ip addr <...> 2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master brq025a9a94-58 state UP qlen 1000 link/ether 00:50:56:a6:b3:78 brd ff:ff:ff:ff:ff:ff inet6 fe80::250:56ff:fea6:b378/64 scope link valid_lft forever preferred_lft forever 4: tap2eb4cad6-cd at if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master brq025a9a94-58 state UP qlen 1000 link/ether 8a:b2:15:4c:96:55 brd ff:ff:ff:ff:ff:ff link-netnsid 0 5: brq025a9a94-58: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000 link/ether 00:50:56:a6:b3:78 brd ff:ff:ff:ff:ff:ff inet 10.20.21.249/24 brd 10.20.21.255 scope global brq025a9a94-58 valid_lft forever preferred_lft forever inet6 fe80::803d:d0ff:fe2e:3ae4/64 scope link valid_lft forever preferred_lft forever 6: tap6d31a191-9f: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master brq025a9a94-58 state UNKNOWN qlen 1000 link/ether fe:16:3e:9a:04:95 brd ff:ff:ff:ff:ff:ff inet6 fe80::fc16:3eff:fe9a:495/64 scope link valid_lft forever preferred_lft forever # brctl showmacs brq025a9a94-58 port no mac addr is local? ageing timer 1 00:50:56:a6:b3:78 yes 0.00 1 00:50:56:a6:b3:78 yes 0.00 2 8a:b2:15:4c:96:55 yes 0.00 2 8a:b2:15:4c:96:55 yes 0.00 3 fe:16:3e:9a:04:95 yes 0.00 3 fe:16:3e:9a:04:95 yes 0.00