Bridge not forwarding the neighbor advertisement

mosquetero

10/10/22, 2:43 PM

I have a bridge created using libvirt and two VMs. I can ping both VMs using ipv4. However, when pinging using ipv6 addresses, it does not work. I can see the neighbor solicitation leaving VM1 and reaching VM2. Then, I can see VM2 replying with a neighbor advertisement. However, the bridge "eats" that packet because I no longer see it in the VM1 link.

tcpdump on the link of VM1:

16:25:57.230617 IP6 2001:db8:42:2::2 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:db8:42:2::1, length 32
16:25:58.250591 IP6 2001:db8:42:2::2 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:db8:42:2::1, length 32
16:25:59.274597 IP6 2001:db8:42:2::2 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:db8:42:2::1, length 32

tcpdump on the link of VM2:

16:26:07.466659 IP6 2001:db8:42:2::2 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:db8:42:2::1, length 32
16:26:07.466859 IP6 2001:db8:42:2::1 > 2001:db8:42:2::2: ICMP6, neighbor advertisement, tgt is 2001:db8:42:2::1, length 32
16:26:08.490685 IP6 2001:db8:42:2::2 > ff02::1:ff00:1: ICMP6, neighbor solicitation, who has 2001:db8:42:2::1, length 32
16:26:08.490914 IP6 2001:db8:42:2::1 > 2001:db8:42:2::2: ICMP6, neighbor advertisement, tgt is 2001:db8:42:2::1, length 32

This is my bridge:

bridge name bridge id       STP enabled interfaces
virbr0      8000.5254001323d4   no      virbr0-nic
                            vnet0
                            vnet1

Note that I have followed this link https://askubuntu.com/a/491752 and configured:

sysctl net.ipv6.conf.virbr0.disable_ipv6=0
sysctl net.ipv6.conf.virbr0.autoconf=1
sysctl net.ipv6.conf.virbr0.accept_ra=1
sysctl net.ipv6.conf.virbr0.accept_ra_defrtr=1

But still, the bridge is not forwarding the neighbor advertisement, only the solicitation

117

1 + 0

ipv6

bridge

linux-networking

Score:1

Server

mosquetero

10/10/22, 2:54 PM

I rebooted everything, executed the sysctl commands and when creating the libvirt network I added

<network ipv6='yes'> as explained in https://libvirt.org/formatnetwork.html#elementsMetadata. Pings are working now

0 + 0

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Bridge not forwarding the neighbor advertisement

TH: สะพานไม่ส่งต่อโฆษณาเพื่อนบ้าน

RO: Bridge nu transmite reclama vecinului

RU: Мост не пересылает объявление соседа

VI: Cầu không chuyển tiếp quảng cáo hàng xóm

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