[c-nsp] ip helper-address, VRF, and Windows 2008 DHCP Server

[Dave Weis]

Hello All

I'm trying to troubleshoot a new network setup. I've got a VRF setup for a client with a couple sites connected via metro Ethernet to replace a VPN.

In this setup I'm trying to use the ip helper-address to relay DHCP requests to a central Windows SBS 2008 DHCP server. Using wireshark I see the requests arriving but the server isn't replying to them. The correct scope is built on the server so I'm wondering if there is something else that needs set on the router to manipulate the packets further before forwarding them.

This is what the subinterface looks like:

interface GigabitEthernet0/1.178
description Customer
encapsulation dot1Q 178
ip vrf forwarding customer-vrf
ip address 10.24.3.254 255.255.255.0
ip helper-address 10.24.1.250
no ip proxy-arp
end

This is what the relayed packet looks like when it hits the DHCP server:

No.     Time        Source                Destination           Protocol Length Info
   3045 5098.662128 10.24.3.254           10.24.1.250           DHCP     351    DHCP Discover - Transaction ID 0x73a7980e

Frame 3045: 351 bytes on wire (2808 bits), 351 bytes captured (2808 bits)
Ethernet II, Src: Cisco_38:a4:1b (00:08:20:38:a4:1b), Dst: Dell_50:34:cd (00:24:e8:50:34:cd)
    Destination: Dell_50:34:cd (00:24:e8:50:34:cd)
        Address: Dell_50:34:cd (00:24:e8:50:34:cd)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Source: Cisco_38:a4:1b (00:08:20:38:a4:1b)
        Address: Cisco_38:a4:1b (00:08:20:38:a4:1b)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Type: IP (0x0800)
Internet Protocol Version 4, Src: 10.24.3.254 (10.24.3.254), Dst: 10.24.1.250 (10.24.1.250)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
    Total Length: 337
    Identification: 0x0ce1 (3297)
    Flags: 0x00
    Fragment offset: 0
    Time to live: 255
    Protocol: UDP (17)
    Header checksum: 0x9393 [correct]
    Source: 10.24.3.254 (10.24.3.254)
    Destination: 10.24.1.250 (10.24.1.250)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
    Source port: bootps (67)
    Destination port: bootps (67)
    Length: 317
    Checksum: 0xc2a6 [validation disabled]
Bootstrap Protocol
    Message type: Boot Request (1)
    Hardware type: Ethernet
    Hardware address length: 6
    Hops: 1
    Transaction ID: 0x73a7980e
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0 (0.0.0.0)
    Your (client) IP address: 0.0.0.0 (0.0.0.0)
    Next server IP address: 0.0.0.0 (0.0.0.0)
    Relay agent IP address: 10.24.3.254 (10.24.3.254)
    Client MAC address: Avaya_86:13:ed (b4:b0:17:86:13:ed)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (t=53,l=1) DHCP Message Type = DHCP Discover
        Option: (53) DHCP Message Type
        Length: 1
        Value: 01
    Option: (t=50,l=4) Requested IP Address = 10.24.1.39
        Option: (50) Requested IP Address
        Length: 4
        Value: 0a180127
    Option: (t=12,l=9) Host Name = "AVX8613ED"
        Option: (12) Host Name
        Length: 9
        Value: 415658383631334544
    Option: (t=55,l=11) Parameter Request List
        Option: (55) Parameter Request List
        Length: 11
        Value: 011c030f060c071a2a2bf2
        1 = Subnet Mask
        28 = Broadcast Address
        3 = Router
        15 = Domain Name
        6 = Domain Name Server
        12 = Host Name
        7 = Log Server
        26 = Interface MTU
        42 = Network Time Protocol Servers
        43 = Vendor-Specific Information
        242 = Private
    Option: (t=57,l=2) Maximum DHCP Message Size = 1000
        Option: (57) Maximum DHCP Message Size
        Length: 2
        Value: 03e8
    Option: (t=60,l=13) Vendor class identifier = "ccp.avaya.com"
        Option: (60) Vendor class identifier
        Length: 13
        Value: 6363702e61766179612e636f6d
    Option: (t=82,l=14) Agent Information Option
        Option: (82) Agent Information Option
        Length: 14
        Value: 020c020a00000a1803fe010000b2
        Agent Remote ID: 020a00000a1803fe010000b2
    End Option

Thanks for any help!
Dave