[c-nsp] IP helper-address source from loopback?

[Arie Vayner (avayner)]

Jay,

Take a look here... I think this should do the trick.
http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iad_dhcps
ervidlink_mcp.html#wp1058967

Arie

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jay Hennigan
Sent: Tuesday, March 20, 2012 07:37
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] IP helper-address source from loopback?

We have a setup where an external global DHCP server is used to assign
pools within a few VRFs on 7206VXR, IOS 12.4.  Interface configuration
looks like this:

interface Port-channel1.3004
 description Test
 encapsulation dot1Q 3004
 ip vrf forwarding net21
 ip address 10.21.97.126 255.255.255.192  ip helper-address global
w.x.y.z

We're using option 82 to communicate the vrf subnet information and it
all works well.

The problem that I'm trying to solve is to use a loopback as the global
source interface from which the DHCP requests originate.  With the above
configuration the router uses the closest egress interface to the DHCP
server.  This is quite usable but I'd prefer it originate on a loopback
for cleanliness and redundancy.

IOS has tweaks to manipulate the source address of telnet, RADIUS, ftp,
tftp, rcmd, and the like but I don't see an obvious way to specify the
source of the DHCP relay packets.

I'm considering attempting a local route-map as a possible solution but
that seems like a pretty big hammer for a small tweak if it works at
all.

Any suggestions from the assorted Cisco wizards?


--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/ Your local
telephone and internet company - 805 884-6323 - WB6RDV
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