ICMP Echo requests initiated from an interface inside VRF don't get ICMP echo replies

Mohamed Kamal

2/8/24, 11:21 AM

I have this setup, which is basically a linux server with one physical interface connected to another device. On this physical interface there is 2 VLANs, 100 and 200. In VLAN100 there is an IP address x.x.x.0/31 configured and enslaved into VRF "TEST". In VLAN200 there is an IP address x.x.x.1/31 configured without any master VRF.

The other device would basically, like a physical cross-connect, flip any incoming frame with VLAN 100 to VLAN 200 and vice versa without inspecting the content.

Now, my problem is, when I try to initiate an ICMP echo request from x.x.x.0 toward x.x.x.1 with the source interface "TEST", I never get an echo reply!

I see that there are ARP request sent from VLAN 100 and reaches VLAN 200, but no ARP replies from VLAN 200 back.

Topology is here

test:~ $ ip addr show eth0.100
269: eth0.100: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9100 qdisc noqueue master TEST state UP group default qlen 1000
    link/ether 52:b6:07:e5:00:0c brd ff:ff:ff:ff:ff:ff
    inet 10.10.10.0/31 scope global eth0.100
       valid_lft forever preferred_lft forever

test:~ $ ip addr show eth0.200
270: eth0.200: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9100 qdisc noqueue state UP group default qlen 1000
    link/ether 52:b6:07:e5:00:0c brd ff:ff:ff:ff:ff:ff
    inet 10.10.10.1/31 scope global eth0.200
       valid_lft forever preferred_lft forever

test:~ $ ip route show 10.10.10.0/31
10.10.10.0/31 dev eth0.200 proto kernel scope link src 10.10.10.1

test:~ $ ip route show 10.10.10.0/31 table 200
10.10.10.0/31 dev eth0.100 proto kernel scope link src 10.10.10.0

test:~ $ ip -br link show type vrf
TEST            UP             8a:50:09:bc:b5:fa <NOARP,MASTER,UP,LOWER_UP>

So what I would expect that, two entries should exist in the ARP table, one for x.x.x.0 and x.x.x.1 with the same mac-address (because it's the same physical interface) but one in a VRF and the other is in the main table. But for some reasons, this doesn't work

What do I miss here?

121

0 + 2

linux

linux-networking

linux-kernel

Romeo Ninov

2/8/24, 11:30 AM

How many IP addresses you have in /31 network?

Mohamed Kamal

2/8/24, 1:00 PM

@RomeoNinov Just 2, so the odd and even, 0 and 1

Elon Musk

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

EN: ICMP Echo requests initiated from an interface inside VRF don't get ICMP echo replies

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