Replies to request coming over a relay goes to relay's internal IP, not to original request's source IP
Oguz Yilmaz
oguzyilmazlist at gmail.com
Sat Oct 6 07:39:19 UTC 2012
Hello,
Dhcpd running on Linux gets a dhcp request over dhcrelay which is
running on other remote machine.
Oct 6 10:09:46 2012 dhcpd: DHCPDISCOVER from 00:1e:68:06:eb:37
(oguz-U300) via 172.16.17.81
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
10:35:01.112500 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF],
proto: UDP (17), length: 328) 192.168.0.81.67 > 192.168.0.1.67:
BOOTP/DHCP, Request from 00:1e:68:06:eb:37, length: 300, hops:1,
xid:0xe378fc7e, flags: [none] (0x0000)
Gateway IP: 172.16.17.81
Client Ethernet Address: 00:1e:68:06:eb:37 [|bootp]
It matches to a subnet and send reply. However reply does not go to
the requesting dhcrelay external IP(192.168.0.81). Instead, it goes to
the internal interface IP of machine running dhcrelay. And I think
because of this remote machine running dhcrelay or the dhcrealy itself
discarding packet.
Oct 6 10:09:46 2012 dhcpd: DHCPOFFER on 172.16.17.11 to
00:1e:68:06:eb:37 (oguz-U300) via 172.16.17.81
10:35:02.050108 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF],
proto: UDP (17), length: 328) 192.168.0.1.67 > 172.16.17.81.67:
BOOTP/DHCP, Reply, length: 300, hops:1, xid:0xe378fc7e, flags: [none]
(0x0000)
Your IP: 172.16.17.11
Gateway IP: 172.16.17.81
Client Ethernet Address: 00:1e:68:06:eb:37 [|bootp]
Is this a normal behaviour?
Machine running dhcrelay:
eth1(ext) Link encap:Ethernet HWaddr 00:90:0B:21:43:F4
inet addr:192.168.0.81 Bcast:192.168.0.255 Mask:255.255.255.0
eth2(int) Link encap:Ethernet HWaddr 00:90:0B:21:43:F5
inet addr:172.16.17.81 Bcast:172.16.17.255 Mask:255.255.255.0
3582 ? Ss 0:00 /usr/sbin/dhcrelay -i eth2 192.168.0.1
Machine running dhcpd:
eth1 Link encap:Ethernet HWaddr 00:90:0B:23:97:D1
inet addr:192.168.0.1 Bcast:192.168.0.255 Mask:255.255.255.0
option domain-name "test.com";
option subnet-mask 255.255.255.0;
authoritative;
ignore client-updates;
ddns-update-style ad-hoc;
default-lease-time 86400;
max-lease-time 86400;
subnet 192.168.0.0 netmask 255.255.255.0 {
range 192.168.0.135 192.168.0.169;
option broadcast-address 192.168.0.255;
option domain-name-servers 192.168.0.1;
option domain-name "test.com";
option routers 192.168.0.1;
}
subnet 172.16.17.0 netmask 255.255.255.0 {
local-address 192.168.0.1;
server-identifier 192.168.0.1;
range 172.16.17.10 172.16.17.11;
option broadcast-address 172.16.17.255;
option routers 172.16.17.81;
}
(I put local-address and server-identifier. But this does not help )
Regards,
--
Oguz YILMAZ
More information about the dhcp-users
mailing list