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HyperBaton

Member

From: Belgium

Registered: 2008-01-18

Posts: 207

Peculiar networking problem with Cisco phone

Okay, this is really doing my head in. I have a bunch of Cisco phones that I want to use in combination with an Asterisk server for our non-profit organization. They don't seem to accept the IP offer being served by the DHCP server, unless I put my laptop in between the switch and the phone as a bridge. This I discovered of course because I wanted to do some packet sniffing on the phone using my laptop as bridge. As soon as I hook up the phone to the switch directly, it's a no go. I've also sniffed the packets sent and received by the phone by mirroring a port on the switch. The DHCP request get sent by the phone and a ACK is sent to the phone. Does anyone have any clue what could be wrong? My brain is starting to feel fried.

Of course, there is no DHCP server running on my laptop, the phone really is getting it's DHCP from the intended server when hooked up to my laptop (it would not register with Asterisk otherwise).

Failure (so without laptop as bridge):

dhcpd on server log:

Jan 16 11:58:26 rt2 dhcpd: DHCPREQUEST for 10.30.6.158 from 00:21:55:04:a0:05 (SEP00215504A005) via eth2
Jan 16 11:58:26 rt2 dhcpd: DHCPACK on 10.30.6.158 to 00:21:55:04:a0:05 (SEP00215504A005) via eth2

tcpdump on server:

11:58:26.986275 IP 10.30.6.158.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:21:55:04:a0:05, length 548
11:58:26.987674 IP 10.30.6.1.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300

Success (with laptop as bridge):

dhcpd on server log:

Jan 16 12:01:32 rt2 dhcpd: DHCPREQUEST for 10.30.6.158 from 00:21:55:04:a0:05 (SEP00215504A005) via eth2
Jan 16 12:01:32 rt2 dhcpd: DHCPACK on 10.30.6.158 to 00:21:55:04:a0:05 (SEP00215504A005) via eth2

tcpdump on server:

12:01:32.233465 IP 10.30.6.158.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:21:55:04:a0:05, length 548
12:01:32.234952 IP 10.30.6.1.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300