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  • #104

Closed
Open
Created Apr 30, 2020 by L6NqLW@L6NqLW

dhcp-relay relays an extra packet with a wrong giaddr

  • Tested on: 4.3.1-6 and 4.4.1-2.
  • Run as: /usr/sbin/dhcrelay -q -4 -a -m discard -i eth0 -i eth1 172.16.0.254
  • Network topology: LAN1 <> eth1_dhcprelay_eth0 <> LAN2
  • DHCP address: 172.16.0.254 (LAN2)
  • dhcprelay_eth0 IP address: 172.16.0.1 (LAN2)
  • dhcprelay_eth1 IP address: 10.10.10.1 (LAN1)

It seems that the dhcp-relay generates and then relays an extra DHCP REQUEST with a wrong GIADDR during RENEW. There are two suspicious behaviors here:

  1. DHCP REQUEST during RENEW is unicast. Why does dhcp-relay touch it?
  2. Why does dhcp-relay put 172.16.0.1 into the GIADDR field? 172.16.0.1 is assigned to the interface where DHCP server is located.
Apr 29 21:07:21 debian dhcpd[2367]: DHCPREQUEST for 10.10.10.10 from 0c:e2:df:02:5a:00 (user) via ens3
Apr 29 21:07:21 debian dhcpd[2367]: DHCPACK on 10.10.10.10 to 0c:e2:df:02:5a:00 (user) via ens3
Apr 29 21:07:21 debian dhcpd[2367]: DHCPREQUEST for 10.10.10.10 from 0c:e2:df:02:5a:00 (user) via 10.10.10.1
Apr 29 21:07:21 debian dhcpd[2367]: DHCPREQUEST for 10.10.10.10 from 0c:e2:df:02:5a:00 (user) via 
172.16.0.1: ignored (not authoritative).
Edited Apr 30, 2020 by L6NqLW
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