The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] RE: Fragmentation in MPLS network BGP problem
I have seen a similar thing therfore my questions
are you using 26xx and7or 36xx routers in you network ?
as those are not fragmenting a packet when the unlabeled packet is below the
MTU size but the labelled packet is above.
It seems that the first fragmentation works giving a 1496 byte frame, but
the answer does not reach the source.
However as far as I know beside PING and TRACEROUTE all applications are
setting the DF-bit and are using path-MTU discovery mechanism.
so maybe try the same thing with DF set and look what messages are comming
back and from which node
with best regards
Alexander
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-----Original Message-----
From: Marcelo Blanes [mailto:mblanes@larc.usp.br]
Sent: Tuesday, October 23, 2001 8:55 PM
To: Robert Raszuk
Cc: mpls-ops@mplsrc.com
Subject: Re: Fragmentation in MPLS network BGP problem
Robert,
See my pings bellow:
For ICMP 1500 ok for 2000 it fails.
The 1500 ping...
PE01#ping
Protocol [ip]:
Target IP address: pe02 (loopback address)
Repeat count [5]:
Datagram size [100]: 1500
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: pe01 (loopback address)
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 10.190.107.251, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
PE01#
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252,
len 1500, rcvd 4
04:45:01: ICMP type=0, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252,
len 1500, rcvd 4
04:45:01: ICMP type=0, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252,
len 1500, rcvd 4
04:45:01: ICMP type=0, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251
PE01#, len 1500, cef process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252,
len 1500, rcvd 4
04:45:01: ICMP type=0, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.252 (local), d=10.190.107.251, len 1500, cef
process switched
04:45:01: ICMP type=8, code=0
04:45:01: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252,
len 1500, rcvd 4
04:45:01: ICMP type=0, code=0
PE01#
The 2000 ping...
PE01#ping
Protocol [ip]:
Target IP address: pe02
Repeat count [5]:
Datagram size [100]: 2000
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: pe01
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 2000-byte ICMP Echos to 10.190.107.251, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
PE01#
05:00:51: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:51: ICMP type=8, code=0
05:00:51: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:51: ICMP type=8, code=0
05:00:51: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252, len
504, rcvd 4
05:00:51: IP Fragment, Ident = 46, fragment offset = 1496
05:00:51: IP: recv fragment from 10.190.107.251 offset 1496 bytes
05:00:53: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:53: ICMP type=8, code=0
05:00:53: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:53: ICMP type=8, code=0
05:00:53: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252, len
504, rcvd 4
05:00:53: IP Fragment, Ident = 47, fragment offset = 1496
05:00:53: IP: recv fragment from 10.190.107.251 offset 1496 bytes
05:00:55: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:55: ICMP type=8, code=0
05:00:55: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:55: ICMP type=8, code=0
05:00:55: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252, len
504, rcvd 4
05:00:55: IP Fragment, Ident = 48, fragment offset = 1496
05:00:55: IP: recv fragment from 10.190.107.251 offset 1496 bytes
05:00:57: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:57: ICMP type=8, code=0
05:00:57: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:57: ICMP type=8, code=0
05:00:57: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252, len
504, rcvd 4
05:00:57: IP Fragment, Ident = 49, fragment offset = 1496
05:00:57: IP: recv fragment from 10.190.107.251 offset 1496 bytes
05:00:59: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:59: ICMP type=8, code=0
05:00:59: IP: s=10.190.107.252 (local), d=10.190.107.251, len 2000, cef
process switched
05:00:59: ICMP type=8, code=0
05:00:59: IP: s=10.190.107.251 (FastEthernet12/0/0), d=10.190.107.252, len
504, rcvd 4
05:00:59: IP Fragment, Ident = 50, fragment offset = 1496
05:00:59: IP: recv fragment from 10.190.107.251 offset 1496 bytes
PE01#
Any light?
Thanks,
Marcelo.
On Sun, 21 Oct 2001, Robert Raszuk wrote:
> Marcelo,
>
> > I have PE - P - PE router. If I do a ping in PE to PE if datagram size
for
> > example 2000 (PE to P router has ether interface if tag mut 1526) with
DF
> > bit not set, I got I timeout answer. For 1500 it work fine.
>
> You would need to narrows down where your packets are being lost. Maybe
> you have a bug of not bumping to process switching (some platforms like
> GSR don't support that at all),
>
> > Ok Robert, but iBGP messages ( session VPNv4 ) is exchange between
> > loopacks. Will iBGP looks to MTU in the loopback?!
>
> No it does not matter what it the IBGP update-src or dst. It matters via
> what PHYSICAL interface the packets are going out of your router, IBGP
> is not aware about any MTU issue. It just passed the generated updates
> to TCP/IP stack and all fragmentatation is done there.
>
> R.
>
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