[c-nsp] ip helper-address, VRF, and Windows 2008 DHCP Server
John Gill
johgill at cisco.com
Wed Jul 27 00:15:23 EDT 2011
Dave,
So you captured this on the DHCP server itself? What is the gateway for
this server configured to do? By default IOS these days does not allow
directed broadcasts, but you do need to configure ip directed-broadcast
on the DHCP server gateway L3 interface. The DHCP DISCOVER should be a
broadcast - perhaps this is why your server doesn't reply to it.
Load-balancers or firewalls in use?
Regards,
John Gill
cisco
On 7/26/11 7:31 PM, Dave Weis wrote:
>
> 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
>
>
>
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