Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Pauljbl]

Hi
I just tried this but the MTU is still 1492 in the ifconfig

[burakkucat]

I seem to remember rather a lot higher numbers being mentioned in respect of BT, for L2 various layers’ PDU sizes - the system has to be able to carry Ethernet including maybe two VLAN tags besides, plus yet more protocol bloat not mentioned too. BT I believe, but memory fails, has a healthy amount of room for additional protocol bloat acquired from lower layers on top of IP PDU MTU of 1500, rather more than the bare minimum iirc.

I suggest that the hardware in use by "BT" (whatever that means) is jumbo frames capable.

I've just taken a quick look at the uplink interface of an Adva FSP150CCf-825 and see "MTU: 9250". If the equipment has jumbo frames ability (and what carrier-class hardware does not have the ability?), it should be used.

[Chrysalis]

you need to bump mtu on the modem as well, not just the router.

[Pauljbl]

I am using the hg612 which everyone says is set for 1508 MTU as standard

[Chrysalis]

I checked my old thread here and yes when I did this on the hg612 I did leave it alone so didnt need to increase the mtu on it, it was in bridge mode.

https://forum.kitz.co.uk/index.php?topic=12842.0

As far as openwrt is concerned tho there is multiple interfaces as has been stated.

You have the individual ethernet interfaces and also the switch interface.  Both would need bumping I think.  I think someone already suggested this to you.

The bridge interface is likely to be named br-lan.

Also on my link I had to do vlan2 also, which was an extra virtual interface assigned to the WAN connection after pppoe was established, its possible openwrt does something similar.    This extra interface doesnt appear until after you connect so is something you change after internet connectivity is established.

I think its eth0.1 you need to set to MTU 1508 based on your ifconfig output.   After thats done try setting the pppoe interface again to 1500.

So try this in order as I am not convinced the bridge needs any adjustment since the lan bridge is not part of the wan connection..

eth0.1 to 1508 then pppoe-wan to 1500
if that fails then set eth0 also to 1508 and try again after pppoe-wan to 1500.

[johnson]

I have not completely given up, but as far as with default OpenWRT on the BT HH5A it will not support 1508 to a modem. I'm sorry for even mentioning it in the thread about OpenWRT devices. 

With any of the release builds you can try:

Code: [Select]

ifconfig eth0 mtu 1508

It will fail with : "ifconfig: SIOCSIFMTU: Invalid argument", which means the driver does not support an MTU higher than 1500.

Last night I compiled a version of 18.06.4 for the HH5A with this patch to lantiq_xrx200.c:

Code: [Select]

static int xrx200_change_mtu(struct net_device *dev, int mtu)
{
if (mtu < 68 || mtu > ETH_DATA_LEN + 8)
return -EINVAL;
dev->mtu = mtu;
return 0;
}

static const struct net_device_ops xrx200_netdev_ops = {
.ndo_init = xrx200_init,
.ndo_open = xrx200_open,
.ndo_stop = xrx200_close,
.ndo_start_xmit = xrx200_start_xmit,
.ndo_set_mac_address = eth_mac_addr,
.ndo_validate_addr = eth_validate_addr,
.ndo_change_mtu = xrx200_change_mtu,

From: https://forum.openwrt.org/t/lantiq-vrx200-pppoe-1500-bytes/4087 (I believe @btsimonh is a user here too)

It compiled without issue and I flashed it to my HH5a, it was now possible to bring up the eth0 interface at 1508 and so a PPPoE connection at 1500. Unfortunately pings with 1472(1500) size then just got lost, no "packet too large" warning, they just fell into a black hole at some point in the chain.

That was as far as I got. Will try again with fresh eyes soon, again apologies for even suggesting the HH5A in the same breath as 1508 compatible modems. It will make a nice wireless AP if you need one?   

[Pauljbl]

At least I know its this router that is the problem.
I was planning on getting another router.

Johnson what thinclient or nuc do you use?

[Chrysalis]

I have not completely given up, but as far as with default OpenWRT on the BT HH5A it will not support 1508 to a modem. I'm sorry for even mentioning it in the thread about OpenWRT devices. 

With any of the release builds you can try:

Code: [Select]

ifconfig eth0 mtu 1508

It will fail with : "ifconfig: SIOCSIFMTU: Invalid argument", which means the driver does not support an MTU higher than 1500.

Last night I compiled a version of 18.06.4 for the HH5A with this patch to lantiq_xrx200.c:

Code: [Select]

static int xrx200_change_mtu(struct net_device *dev, int mtu)
{
if (mtu < 68 || mtu > ETH_DATA_LEN + 8)
return -EINVAL;
dev->mtu = mtu;
return 0;
}

static const struct net_device_ops xrx200_netdev_ops = {
.ndo_init = xrx200_init,
.ndo_open = xrx200_open,
.ndo_stop = xrx200_close,
.ndo_start_xmit = xrx200_start_xmit,
.ndo_set_mac_address = eth_mac_addr,
.ndo_validate_addr = eth_validate_addr,
.ndo_change_mtu = xrx200_change_mtu,

From: https://forum.openwrt.org/t/lantiq-vrx200-pppoe-1500-bytes/4087 (I believe @btsimonh is a user here too)

It compiled without issue and I flashed it to my HH5a, it was now possible to bring up the eth0 interface at 1508 and so a PPPoE connection at 1500. Unfortunately pings with 1472(1500) size then just got lost, no "packet too large" warning, they just fell into a black hole at some point in the chain.

That was as far as I got. Will try again with fresh eyes soon, again apologies for even suggesting the HH5A in the same breath as 1508 compatible modems. It will make a nice wireless AP if you need one?   

Think I have hit the same roadblock, I believe the solution is using your patched firmware, (if you could do one for 19.07 would be great) combined with a usb ethernet device, so the 1508 can be set on the dsl device, and then its bridged to the usb ethernet device.