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BGP PMTUD on Huawei NE ?

Latest reply: Dec 28, 2017 11:33:16 2313 3 0 0 0
Hi guys,

Does anyone test the BGP PMTUD on Huawei NE20 and NE40 on iBGP peers? The Huawei behaviour is different than Cisco, especially on v8.120 on NE20.

* When BGP PMTUD is disabled on both peers, BGP MSS is still 8960 (when all interface MTUS are 9000). If discovery is disabled, an interface MTU on the path can be default (as 1500) so this shouldnt be 8960 as my understanding on RFC.

* When BGP PMTUD is enabled and some interface MTUs on path are changed to 6000; 
**  the v8.120 shows MSS as 1460 (which is not OK), 
**  the v5.160 shows MSS as 5960 (which is OK).

Huawei NE20E        Version 8.120 (NE20E V800R008C10SPC300)

Huawei NE40E        Version 5.160 (NE40E&80E V600R008C10SPC300)

Not: Also icmp protocol 1 is permittedon all devices.

Is there any difference on default config between the peers? Or what is the Huawei behaviour on BGP PMTUD?


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Created Dec 12, 2017 05:54:52

please wait for help!
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Created Dec 18, 2017 06:20:58

1、MTU=MSS+TCP Header+IP Header
2、Default config of PMTU is the same
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Created Dec 28, 2017 11:33:16

I know what is BGP PMTUD and how it works on other vendors. For ex, Huawei behavior is not same as Cisco. On Cisco; When BGP PMTUD is disabled, the minimum BGP MSS is 536 bytes. When BGP PMTUD is enabled, BGP MSS is "pathmtu-TCPheader-IPheader".

I opened a case to Huawei and I couldnt get a proper answer that what the Huawei behavior is on BGP PMTUD. I did multiple tests, but even the PMTUD is disabled, BGP MSS is 8960 on most neighbors (far end neigbors and interface MTU is 9000). If PMTUD is disabled, router should use a default minimum MSS value for this not the physical interface MTU parameter to calculate MSS.

My question is if anyone did some tests about BGP PMTUD feature, also Huawei NE behaviour?

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