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
Does BGP try to perform MTU path-discovery? Do I need to worry regarding fragmentation problems? Thanks, Marcelo. On Wed, 24 Oct 2001, Alexander Marhold wrote: > 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 > > __/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/__/ > __/ > __/ Dipl.Ing. Alexander Marhold MBA > __/ CCIE #3324, CCNP, CCDP, CCSI #20642 > __/ Core & IP Services <Senior Consultant> > __/ Mobile: ++43-(0)664-16 28 234 > __/ PRO IN http://www.proin.com > > > > -----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. > > > > ------- > > The MPLS-OPS Mailing List > > Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml > > Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > > > > ------- > The MPLS-OPS Mailing List > Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml > Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > > ------- > The MPLS-OPS Mailing List > Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml > Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > ------- The MPLS-OPS Mailing List Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml Archive: http://www.mplsrc.com/mpls-ops_archive.shtml
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