why on earth don't I get an ARP reply from this VRRP enabled router?

Openbaar
,
1

Hi,

I’ve got a VPS. That VPS talks to the world via some VRRP enabled router. The virtual address is .254 and its legs are on .252 and .253.
When I ask .252 or .253 its mac-address via arp, I get an answer. If I ask .254 for its mac address it doesn’t respond at all (yet I can ping it?!).
“just route via 252 or 253” one would say; only that doesn’t seem to work (have not figured out that yet)
I verified the arp-requesting-stuff using arping:

arping 94.142.246.253 -S 94.142.246.161

Any ideas?

example network trace

2

Can’t ping without arp…

1 Like
3

Is The .254 in Your ARP table?

The router certainly sent out a gratuitous ARP packet.

4

Wait, let me redo my tests.

On the vps I run in one window:

while true ; do arp -i enp8s0 -d 94.142.246.254 ; arp -i enp1s0 -d 94.142.246.254 ; arp -an | grep 254 ; ping -q -c 1 8.8.8.8 ; arp -an | grep 254 ; sleep 1 ; done

in the other I run tcpdump.

tcpdump -i enp1s0 -n -w /root/test.pcap \! port 655

(port 655 is the vpn, I filter it to reduce the noise).

If I then examine the dump, then I see no arp responses at all, only the requests?! (tcpdump -r /root/test.pcap -n arp)

How on earth does the linux system then get to know the mac-address of the gw?