host-identifier option problem

Sten Spans sten at
Fri Feb 20 14:32:27 UTC 2015

We've been quite happily using the option82 support with
ISC DHCPD 4.2.6 and a configuration similar to the following:

ubnet  netmask {
     option domain-name  "mydomain";

host foobar {
     option host-name "foobar";
     host-identifier option agent.circuit-id "mccx-c1-p1-sw1";
     default-lease-time infinite;
     max-lease-time infinite;

However we are now trying to configure option 82 on arista switches
and seem to have hit a snag. The dhcp daemon is refusing to hand out 
leases to hosts matching the configured circuit-id's. The only difference
seems to be that arista switches generate requests with only a circuit-id, 
but no remote-id.

Packets look like the following: > BOOTP/DHCP, Request from 
00:1c:73:40:74:35 (oui Unknown), length 277, hops 2, xid 0x5598377c, Flags 
 	  Client-Ethernet-Address 00:1c:73:40:74:35 (oui Unknown)
 	  Vendor-rfc1048 Extensions
 	    Magic Cookie 0x63825363
 	    DHCP-Message Option 53, length 1: Discover
 	    Parameter-Request Option 55, length 13:
 	      Subnet-Mask, BR, Time-Zone, Classless-Static-Route
 	      Domain-Name, Domain-Name-Server, Hostname, YD
 	      YS, NTP, MTU, Option 119
 	    Agent-Information Option 82, length 16:
 	      Circuit-ID SubOption 1, length 14: mccx-c1-p1-sw1

Note the missing remote-id. The result on the dhcpd side seems to be:

Feb 20 14:32:07 tlamdns2 dhcpd: DHCPDISCOVER from 00:1c:73:40:74:35 circuit-id mccx-c1-p1-sw1 via network no free leases

However if I manually generate a request (via tcpreplay)
which looks like this: > BOOTP/DHCP, Request from 
Request from e8:39:35:26:63:8e (oui Unknown), length 324, hops 1, xid 0x8, 
secs 28, Flags [none]
 	  Client-Ethernet-Address e8:39:35:26:63:8e (oui Unknown)
 	  Vendor-rfc1048 Extensions
 	    Magic Cookie 0x63825363
 	    DHCP-Message Option 53, length 1: Discover
 	    Client-ID Option 61, length 7: ether e8:39:35:26:63:8e
 	    Parameter-Request Option 55, length 15:
 	      Subnet-Mask, Time-Zone, Default-Gateway, Time-Server
 	      Domain-Name-Server, Domain-Name, BR, Static-Route
 	      NTP, Vendor-Option, Netbios-Name-Server, RN
 	      RB, PRTR, MDHCP
 	    Agent-Information Option 82, length 32:
 	      Circuit-ID SubOption 1, length 14: mccx-c1-p1-sw1
 	      Remote-ID SubOption 2, length 9: ^A^Gmccxsw5

Then I get:

Feb 20 14:37:14 mccmdns2 dhcpd: DHCPDISCOVER from e8:39:35:26:63:8e circuit-id mccx-c1-p1-sw1 remote-id 1:7:6d:63:63:78:73:77:35 via
Feb 20 14:37:14 mccmdns2 dhcpd: DHCPOFFER on to e8:39:35:26:63:8e via

Anybody got a clue what's going wrong here?
I've been trying to spot the issue using the source,
but haven't been able to come up with anything so far.

Sten Spans

"There is a crack in everything, that's how the light gets in."
Leonard Cohen - Anthem

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