ip virtual-reassembly Problem.

[mohamednselim]

Dear all,

Please i have been having these logging:

*Jun  4 06:52:20.366: %IP_VFR-4-FRAG_TABLE_OVERFLOW: FastEthernet0/1: the fragment table has reached its maximum threshold 32
*Jun  4 07:00:31.574: %IP_VFR-4-FRAG_TABLE_OVERFLOW: FastEthernet0/0: the fragment table has reached its maximum threshold 16
 

First I don't understand the different between Ip virtual-reassembly in and out. 

when I configured the interfaces the default is in.

i can see it with show ip virtual-reassembly (interface).

here is my interfaces config:

interface FastEthernet0/0
 description <<""Inside"">>
 ip address  x.x.x.x 255.255.255.0
 ip pim sparse-mode
 ip nat inside
 ip virtual-reassembly
 duplex auto
 speed auto
!
interface FastEthernet0/1
 description <<""Internet"">>
 ip address Real IP address
 ip nat outside
 ip virtual-reassembly
 duplex auto
 speed auto

And here is my show ip virtual-reassembly for my both interfaces.

#sh ip virtual-reassembly fa 0/0
FastEthernet0/0:
   Virtual Fragment Reassembly (VFR) is ENABLED [in]
   Concurrent reassemblies (max-reassemblies): 16
   Fragments per reassembly (max-fragments): 32
   Reassembly timeout (timeout): 3 seconds
   Drop fragments: OFF

   Current reassembly count:0
   Current fragment count:0
   Total reassembly count:6364092
   Total reassembly timeout count:3

sh ip virtual-reassembly fa 0/1
FastEthernet0/1:
   Virtual Fragment Reassembly (VFR) is ENABLED [in]
   Concurrent reassemblies (max-reassemblies): 16
   Fragments per reassembly (max-fragments): 32
   Reassembly timeout (timeout): 3 seconds
   Drop fragments: OFF

   Current reassembly count:0
   Current fragment count:0
   Total reassembly count:10985
   Total reassembly timeout count:1533

And when the messages start to appear in the logging the Internet start to get really slow.

Please help me with this problem. 

Thanks and regards,

Mohamed Selim.

[Hitesh Vinzoda]

Hi there,

Prima facie it looks like MTU problem, as there is fragmentation happening, Check for MTU along the path.

HTH

Hitesh

[mohamednselim]

Dear Hitesh,

My MTU on both interfaces is 1500,

when I open the drop fragment on the interfaces the message is gone..

And my ISP MTU is 1700.

Thanks and regards,

Mohamed Selim.

[Hitesh Vinzoda]

Hi,

Ping from a PC behind the router using option -f -l 1500 and see if makes through to find out path MTU to google or any public IP on the network. Also try extending the buffers on the interface.

ip virtual-reassembly max-fragments xxx max-reassemblies xxx 

also you can check your MTU online 

http://www.letmecheck.it/mtu-test.php

HTH

Hitesh

[mohamednselim]

hi,

here is what appeared to me

Pinging 8.8.8.8 with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 8.8.8.8:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

And this is my new config now under the interfaces:

interface FastEthernet0/0
 description <<""Inside"">>
 ip address x.x.x.x 255.255.255.0
 ip pim sparse-mode
 ip nat inside
 ip virtual-reassembly in drop-fragments timeout 5
 duplex auto
 speed auto
!
interface FastEthernet0/1
 description <<""Internet"">>
 ip address Real IP
 no ip proxy-arp
 ip nat outside
 ip virtual-reassembly in drop-fragments timeout 5
 duplex full
 speed 100

and here is the show ip virtual

#sh ip virtual-reassembly 
FastEthernet0/0:
   Virtual Fragment Reassembly (VFR) is ENABLED [in]
   Concurrent reassemblies (max-reassemblies): 16
   Fragments per reassembly (max-fragments): 32
   Reassembly timeout (timeout): 5 seconds
   Drop fragments: ON

   Current reassembly count:0
   Current fragment count:0
   Total reassembly count:0
   Total reassembly timeout count:0

FastEthernet0/1:
   Virtual Fragment Reassembly (VFR) is ENABLED [in]
   Concurrent reassemblies (max-reassemblies): 16
   Fragments per reassembly (max-fragments): 32
   Reassembly timeout (timeout): 5 seconds
   Drop fragments: ON

   Current reassembly count:0
   Current fragment count:0
   Total reassembly count:0
   Total reassembly timeout count:0

Thanks.

[syed kazim abbas]

hi,

see these discussion:

https://supportforums.cisco.com/discussion/10350421/ipvfr-3-overlapfragments

https://supportforums.cisco.com/discussion/11027121/ipvfr-4-fragtableoverflow

Regards,

kazim