[j-nsp] BGP tcp-mss

Mon Mar 22 15:41:05 EDT 2010

Guys;
 I ran into this issue sometime ago, and basically all you can do is configured the "tcp-mss" under the bgp session or ask your transmission dept to increase their mtu on the transport side (if supported). Majority of transmission techs aren't aware of this setting so you'll have to ask them to research it with equipment manufacturer. 

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of david.roy at orange-ftgroup.com
Sent: Monday, March 22, 2010 3:30 PM
To: 'Harry Reynolds'; juniper-nsp at puck.nether.net
Subject: Re: [j-nsp] BGP tcp-mss

Hi,

Just for info. A new PR 514196 has been opened to track this issue.

Regards,
David

David Roy
Orange France - RBCI IP Technical Assistance Center
Tel.   +33(0)299876472
Mob. +33(0)685522213
Email. david.roy at orange-ftgroup.com

-----Message d'origine-----
De : Harry Reynolds [mailto:harry at juniper.net] 
Envoyé : mercredi 3 février 2010 17:10
À : ROY David DTF/DERX; juniper-nsp at puck.nether.net
Objet : RE: BGP tcp-mss

I believe so. I only scanned, but did not seem platform or pmtu related.

Regards

-----Original Message-----
From: david.roy at orange-ftgroup.com [mailto:david.roy at orange-ftgroup.com]
Sent: Wednesday, February 03, 2010 2:39 AM
To: Harry Reynolds; juniper-nsp at puck.nether.net
Subject: RE: BGP tcp-mss

Hi,

Path MTU Discovery is disabled and I have the problem with MX, T640 and T1600 platforms. 
Do you think that the PR might include my case as well ? 

Regards,
David

David Roy
Orange France - RBCI IP Technical Assistance Center
Tel.   +33(0)299876472
Mob. +33(0)685522213
Email. david.roy at orange-ftgroup.com

-----Message d'origine-----
De : Harry Reynolds [mailto:harry at juniper.net] Envoyé : mercredi 3 février 2010 02:22 À : ROY David DTF/DERX; juniper-nsp at puck.nether.net Objet : RE: BGP tcp-mss

Sounds like case 2009-0127-0051, which seems to have been fixed via pr 390993 around 9.4.

Hths

Harry

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of david.roy at orange-ftgroup.com
Sent: Tuesday, February 02, 2010 6:55 AM
To: juniper-nsp at puck.nether.net
Subject: [j-nsp] BGP tcp-mss

Hi all,

Do you why, when I set the tcp-mss to 4096 between to BGP neighbors, this one is well exchange between the TCP Connection Establishment but when I check the mss via the command "show system connection extensive" I see that the mss used is 2048 (the half).

R1 config - lo0 172.20.223.6 :

  neighbor 172.20.223.5 {
        tcp-mss 4096;
    }
R2 config - lo0 172.20.223.5

  neighbor 172.20.223.6 {
        tcp-mss 4096;
    }

One Link between R1 and R2 with MTU set to 4484.

TCPDUMP output on R2 - we see that 4096 is well exchanged :

15:49:29.681732 Out IP 172.20.223.5.55025 > 172.20.223.6.179: S 2338565447:2338565447(0) win 16384 <mss 4096,nop,wscale 0,nop,nop,timestamp 2417320394 0,sackOK,eol>
15:49:29.682439  In IP 172.20.223.6.179 > 172.20.223.5.55025: S 1139135010:1139135010(0) ack 2338565448 win 16384 <mss 4096,nop,wscale 0,nop,nop,timestamp 455578404 2417320394,sackOK,eol>
15:49:29.682455 Out IP 172.20.223.5.55025 > 172.20.223.6.179: . ack 1 win 16384 <nop,nop,timestamp 2417320394 455578404>

On R2 : show system connection extensive | find 172.20.223.6

tcp4       0      0  172.20.223.5.55025                            172.20.223.6.179                              ESTABLISHED
   sndsbcc:          0 sndsbmbcnt:          0  sndsbmbmax:     131072
sndsblowat:       2048 sndsbhiwat:      16384
   rcvsbcc:          0 rcvsbmbcnt:          0  rcvsbmbmax:     131072
rcvsblowat:          1 rcvsbhiwat:      16384
   proc id:       1131  proc name:        rpd
       iss: 2338565447      sndup: 2338567245
    snduna: 2338567245     sndnxt: 2338567245      sndwnd:      16384
    sndmax: 2338567245    sndcwnd:       4096 sndssthresh: 1073725440
       irs: 1139135010      rcvup: 1139136242
    rcvnxt: 1139136261     rcvadv: 1139152645      rcvwnd:      16384
       rtt:          0       srtt:       2230        rttv:        574
    rxtcur:       1200   rxtshift:          0       rtseq: 2338567226
    rttmin:       1000  mss:       2048

N.B: Release 9.3

Thank you
Regards,
David

David Roy
Orange France - RBCI IP Technical Assistance Center
Tel.   +33(0)299876472
Mob. +33(0)685522213
Email. david.roy at orange-ftgroup.com<mailto:david.roy at orange-ftgroup.com>

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