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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