Cisco DHCP Server Support for MPLS VPNs??


Hi group,

Been playing with DHCP and its various configurations today and came up against some pain when trying to implement the configs in “DHCP Relay Agent Support for MPLS VPNs”. The issue I’m having is I can configure the Relay Agent to send the VPN sub-options to the DHCP server, but I can’t get the DHCP server to allocate an IP address from the VPN-specific pool. See topology below:

Please view in a fixed-width font such as Courier.

| 10.1.1.1/24 | +—+ +—+ | +——+R3 | |R1 +——–+ 10.1.1.2/24 10.1.2.2/24| +—+ +—+ | vrf: Global +—+ vrf: RED | +————-+R2 +————+ DHCP Server | +—+ | DHCP Clients Cisco IOS | | DHCP Relay | +—+ Agent +——+R4 | Cisco IOS | +—+

R1 config:

ip dhcp pool NET-2-RED vrf RED network 10.1.2.0 255.255.255.0 default-router 10.1.2.2 dns-server 192.168.100.100 domain-name relay.com

ip vrf RED rd 1:1 route-target export 1:1 route-target import 1:1 !

R2 config:

ip dhcp relay information option

ip vrf RED rd 1:1 vpn id 1:1 route-target export 1:1 route-target import 1:1

interface FastEthernet0/1 ip dhcp relay information option vpn-id ip vrf forwarding RED ip address 10.1.2.2 255.255.255.0 ip helper-address vrf global 10.1.1.1

Now, when R3 or R4 attempts to get an address via DHCP, R2 sends the request to R1 with VPN sub-options:

(R2 debug output) R2#sh debugging DHCP server event debugging is on. DHCPC: DHCP client activity debugging is on (detailed)

*Mar 1 00:56:23.423: DHCPD: htype 1 chaddr c402.0a04.0001 *Mar 1 00:56:23.427: DHCPD: remote id 020a00000a01020201000000 *Mar 1 00:56:23.427: DHCPD: circuit id 00000000 *Mar 1 00:56:23.431: DHCPD: table id 1 = vrf RED *Mar 1 00:56:23.431: DHCPD: VPN id =1:1 *Mar 1 00:56:23.435: DHCPD: Selected subnet=10.1.2.0 *Mar 1 00:56:23.435: DHCPD: Server-id-override=10.1.2.2 *Mar 1 00:56:23.439: DHCPD: giaddr changed to 10.1.1.2 *Mar 1 00:56:56.663: DHCPD: Sending notification of DISCOVER: *Mar 1 00:56:56.663: DHCPD: htype 1 chaddr c402.0a04.0001 *Mar 1 00:56:56.667: DHCPD: remote id 020a00000a01020201000000 *Mar 1 00:56:56.667: DHCPD: circuit id 00000000 *Mar 1 00:56:56.671: DHCPD: table id 1 = vrf RED *Mar 1 00:56:56.671: DHCPD: Seeing if there is an internally specified pool class:

But R1 complains that it doesn’t have an address pool for R2’s address on the 10.1.1.0/24 subnet (i.e. the subnet between R1 & R2)

(R1 debug output) R1#sh debugging DHCP server event debugging is on. DHCPC: DHCP client activity debugging is on (detailed)

*Mar 1 00:58:26.823: DHCPD: Sending notification of DISCOVER: *Mar 1 00:58:26.823: DHCPD: htype 1 chaddr c402.0a04.0001 *Mar 1 00:58:26.827: DHCPD: remote id 020a00000a01010100000000 *Mar 1 00:58:26.827: DHCPD: circuit id 00000000 *Mar 1 00:58:26.831: DHCPD: Seeing if there is an internally specified pool class: *Mar 1 00:58:26.831: DHCPD: htype 1 chaddr c402.0a04.0001 *Mar 1 00:58:26.835: DHCPD: remote id 020a00000a01010100000000 *Mar 1 00:58:26.835: DHCPD: circuit id 00000000 *Mar 1 00:58:26.839: DHCPD: there is no address pool for 10.1.1.2.

This is driving me quite batty at the moment! The only thing I can think of is that IOS can’t act as the DHCP server when using the VPN sub-options. Does anyone have any suggestions/experience with this feature??

Cheers, Gavin

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