DHCP Relay won't work on a Virtual-Template Interface

[Liam Ferguson]

Hi

Hope you can help me out

I am trying to achieve the following scenario

These two parts are working

PPP user --> LNS Router -->Radius

Radius --> LNS Router

I am having trouble getting this part working

LNS Router --> DHCP Relay

interface Loopback2
 ip address 10.10.10.10 255.255.255.0

interface Virtual-Template1
 ip unnumbered Loopback2
 ip helper-address 1.1.1.1
 ip mtu 1400
 ip tcp adjust-mss 1360
 peer default ip address dhcp
 ppp mtu adaptive
 ppp authentication pap chap
 ppp chap hostname router1
 ppp ipcp dns 2.2.2.2 3.3.3.3
end

With the above config, my debug dhcp detail looks something like this

Feb 22 14:04:58.191: DHCP: SDiscover attempt # 1 for entry:
Feb 22 14:04:58.191: DHCP: SDiscover: sending 285 byte length DHCP packet
Feb 22 14:04:58.191: DHCP: SDiscover 285 bytes
Feb 22 14:04:58.191:             B'cast on Port-channel1.122 interface from 10.10.10.10
Feb 22 14:04:58.191:             B'cast on Port-channel2.312 interface from 10.10.10.10

Note: Why would this DHCP Request be broadcast on two other Layer 3 interfaces when in theory it should be only broadcast on the 10.10.10.0/24 subnet?? Neither Port-channel1.122  or Port-channel1.312 are in the 10.10.10.0/24 subnet

The DHCP server (1.1.1.1) isn't showing up in the debugs and there are only mentions of Broadcast so I suspect the DHCP is being generated (using this command  peer default ip address dhcp) but the helper address command isn't converting it to unicast.

Any ideas and feedback would be very helpful

Thank you in advance

[Georg Pauwen]

Hello,

do you see the same behavior when you configure the virtual template with 'virtual profile if-needed' ?

What is the output of 'show interfaces virtual-access' ?

[Liam Ferguson]

Hi Georg

Thanks for the replay. I added that command but I am still seeing the same issue.

Virtual Access 1 is down  but 2 is up

Virtual-Access2 is up, line protocol is up
  Hardware is Virtual Access interface
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Closed
  Base PPPoVPDN vaccess
  Vaccess status 0x44, loopback not set
  Keepalive set (10 sec)
  DTR is pulsed for 5 seconds on reset
  Last input never, output never, output hang never
  Last clearing of "show interface" counters 5w0d
  Input queue: 0/4096/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     176962 packets input, 61890325 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     381334 packets output, 159289892 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions

Liam

[Georg Pauwen]

Hello Liam,

try to configure 'ip directed-broadcast' on the virtual template.

[Liam Ferguson]

Hi Georg

Thank you

Just tried that but it's still sending out the Broadcast DHCP instead of directed unicast

Liam

[Liam Ferguson]

I found a way to get this working.

When the interface sub commands wouldn't work, I turned to global commands instead.

What I did was create a global reference to a dhcp server using

ip dhcp-server 1.1.1.1

After this, the DHCP request was no longer broadcasted out. It went out as a directed unicast and I picked up an IP OK

Just to follow it through though I removed the

 ip helper-address 1.1.1.1

command and it still worked proving that the global command overrules the ip helper in this case.

Thanks Georg for your help on this

Any other suggestions still welcome as to how this can be done under the interface and not globally

Liam