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I have a following network topology:

ARP and SNAT

Sometimes I see ARP requests from server which request MAC address for IPv4 address which is not in the broadcast domain:

18:37:01.707771 00:16:3e:1a:61:b5 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.0.251 tell 10.10.10.15, length 28
18:37:01.708165 00:16:3e:62:9f:51 > 00:16:3e:1a:61:b5, ethertype ARP (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply 192.168.0.251 is-at 00:16:3e:62:9f:51, length 46

Why do hosts(192.168.0.251 in example above) reply to such ARP requests? I would expect them to simply ignore such requests.

  • You have a network segment with two netblocks, the MAC in the ARP request matches the interface ...Is this a linux question? – Rui F Ribeiro Jan 30 '17 at 19:44
  • Apparently MAC 00:16:3e:62:9f:51 thinks it is assigned this address, and it even answers. Which interface does this MAC belong to? Which interface does 00:16:3e:1a:61:b5 belong to? – dirkt Jan 31 '17 at 13:13

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