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Jumbo frames on LAN vs IPv6 on WAN

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Jumbo frames on LAN vs IPv6 on WAN

My LAN uses 10 Gigabit network equipment. All the PCs and switches support 9KB jumbo frames. This is required to achieve decent level of performance between machines, such as LAN backups. We are talking performance going from sub 1 Gb/s to >4 Gb/s on the LAN when jumbo frames are enabled.

 

Everything is fine with Internet packets as long as only IPv4 is enabled on the router and PCs.

The moment IPv6 is enabled though, things break down with IPv6 large packets speed tests on the LAN PCs that use jumbo frames.  Switching back to regular 1500 bytes frames fixes the issue with IPv6 on WAN, but kills network performance on the LAN to LAN side ...


I tried to take the router and switches completely out of the equation, ie. connecting the PC with jumbo frames enabled directly to the modem (Arris SB8200) , and the problem with IPv6 large packet tests failing remains the same.

It's not just those tests that fail actually. I can't even login to this forum at all when IPv6 and jumbo frames are enabled. The TLS handshake with login.comcast.net fails unless either jumbo frames or IPv6 are disabled.

 

Questions :

1) a) is there a way to configure the Arris SB8200 modem to enable 9KB jumbo frames on its ethernet port ?

b) if yes, will that work with the Comcast cable network ?

 

2) assuming 1) is not possible,  is there a way to configure network equipment in between the LAN in a way that I can still keep jumbo frames and IPv6 enabled on my LAN machines,  but not experience major internet breakage ?

I have a Trendnet TEG-7080ES 10 Gb switch which allows me to configure jumbo frames on/off for each 10 Gb LAN port.

My router is  a Ubiquiti USG-3P which doesn't officially support jumbo frames or MTU >1500, but those can be enabled via CLI. I haven't been successful so far, though.

More gory details at :
https://community.ui.com/questions/USG-vs-IPv6-and-jumbo-frames-on-LAN/330e4505-e0d8-4e96-bd32-89df6...

Unfortunately the Ubiquiti experts were no help.

 

I'm open to trying another IP router if one can deal with this situation of 9KB frames on LAN and 1.5KB frames on WAN in a better way.

FYI, with my current config, these are the test results at http://test-ipv6-vm4.comcast.net/ :

Test with IPv4 DNS record  
ok (0.078s) using ipv4
Test with IPv6 DNS record  
ok (0.106s) using ipv6
Test with Dual Stack DNS record  
ok (0.070s) using ipv6
Test for Dual Stack DNS and large packet  
ok (2.452s) using ipv6
Test IPv4 without DNS  
ok (0.086s) using ipv4
Test IPv6 without DNS  
ok (0.090s) using ipv6
Test IPv6 large packet  
timeout (5.382s)
Test if your ISP's DNS server uses IPv6  
ok (0.101s) using ipv6
Find IPv4 Service Provider  
ok (0.037s) using ipv4 ASN 7922
Find IPv6 Service Provider  
ok (0.025s) using ipv6 ASN 7922


Same result with PC directly connected to cable modem, or going through switch & router.

With the later config, the hardware is :

Windows 10 desktop PC with AQN-107 10 gb cards. 9 KB  MTU, ie. jumbo frames enabled . Connected to port 7 of 10Gb switch.
Ubiquiti USG-3P LAN port connected to port 3 of 10 Gb switch. 1500 MTU 
Ubiquiti USG-3P WAN port connected to port SB8200 . 1500 MTU
Arris SB8200 with default config (no MTU option in admin UI, presumably 1500).
Trendnet TEG-7080ES switch has jumbo frames enabled for port 7 (supports 9KB max).
Trendnet TEG-7080ES switch has jumbo frames disabled for port 3.


Failures with Ipv6 with the above config are exactly the same as :
Windows 10 desktop PC with AQN-107 10 gb cards. 9 KB  MTU, ie. jumbo frames enabled . Connected to LAN port of Arris SB8200
Arris SB8200 with default config (no MTU option in admin UI, presumably 1500).