Kitz Forum
Broadband Related => Broadband Hardware => Topic started by: Pauljbl on August 08, 2019, 08:45:16 AM
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Is a MTU of 1508 possible on the hg612 if so is configured on the router as don't see settings for MTU on the modem webui
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It does MTU 1500 by default (1508).
How to test:
LINUX:
ping -c4 -M do -s 1472 1.1.1.1
WINDOWS:
ping -f -l 1472 9.9.9.9
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Packet size 1472 will be allowed and not fragmented if you have a standard 1500 MTU, which is what you are after.
If you try 1473 it will fail.
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Hi
It’s worth mentioning that if your dsl supplier does not support 1500 mtu, then your tests would fail. If supplier supports 1500 mtu, test would pass
The hg612 requires no changes as it is capable of 1500 mtu
Many thanks
John
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1464 is the highest I can go
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Hi
So you mtu is 1492 which is standard for most dsl providers
Many thanks
John
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Does the hg612 have a settings for MTU if needed changing
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Hi
I would not change mtu on hg612
Are you still using hg612 as router/modem
If so, I personally would not as it does not have enough power in my view but works lovely as bridge modem
Many thanks
John
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Have it in router mode but planning on putting it in bridged mode
I don't plan on changing the MTU just wondered out of interest how you would change it as can't see any settings for it?
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Is the MTU on the hg612 set automatically or does it set by the router bit confused about it. If the hg612 is 1500 MTU and I have 1492 does it auto adjust to the max mtu
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Does the higher 1500 MTU make much of a difference in speed?
Packet size 1472 will be allowed and not fragmented if you have a standard 1500 MTU, which is what you are after.
If you try 1473 it will fail.
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Does the higher 1500 MTU make much of a difference in speed?
1464 bytes to 1472 bytes is only a 0.55% increase.
It might be possible to use the HG612 in router mode with 1500 MTU with a few short commands.
I don't recommend the HG612 in router mode on FTTC unless you have a very low sync speed.
It doesn't have the guts to do higher speeds when doing PPP/routing at the same time.
On my old 80/20 line the HG612 (in router mode) wouldn't get anywhere near 80Mb, struggled to maintain 40Mb, and dropped down to 20Mb when uploading.
Great modem, not designed to be used as a router though.
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Not really, we are talking about a 0.54% difference in packet size.
Its more about compliance and being technically correct. If the whole internet runs on 1500 why would you want your connection to run at 1492.
The worst case scenario is that < 1500 MTU will cause packet fragmentation and double overheads and such, but they are usually well mitigated by PMTUD and MSS clamping. But you are reliant on the whole network complying with the relevant RFCs.
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I took care to get my dsl modems etc to be all MTU 1508 compliant but as earlier posters have said, it’s only a minute speed improvement and it is really for me about dotting i’s in standards compliance (I am a pedant, I suppose).
And then my Huawei 3G USB NIC goes and ruins the whole thing by not speaking anywhere near MTU 1500 even, and worse, not speaking IPv6 so that I need to use 20-byte wasting IPv4 proto41 headers for all IPv6 traffic while using the 3G NIC in failover mode. So for failover I use IPv6 MTU of 1408 now (that is, IPv6 PDU size = 1408).
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I was able to use an MTU of 1508 on pfSense fine using the HG612.
I never understood how it worked as the HG612 interfaces showed 1500 yet I got no fragmentation errors.
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Remember that 1508 is inclusive of PPPoE header and 1500 is exclusive; 1500 is just the IP PDU ie IP packet including IP header and payload. So 1508 is an MTU for PPP and 1500 is an MTU for IP PDUs. Just in case anyone was confused. They’re probably more confused now.
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As others have mentioned, the HG612 can handle baby jumbo frames in bridged mode without needing any additional configuration.