MER / MTU / Respond to Ping???

Before getting sky I had a normal router (Netgear DG834G) and had the pc and router mtu set to 1458.

So got sky and set their router mtu to 1458...

A week later the router updates its firmware from 1.11 to 2.04 and am now connected to mer instead of pppoa. the mtu on the router can no longer be changed and is hard set to 1500.

Ok, so I try setting the pc mtu to 1500, it says ok but on a reset it goes back to 1458.

I set it by running cmd as admin and paste this ... netsh interface ipv4 set subinterface "Local Area Connection" mtu=1500 store=persistent

But it just keeps going back to 1458

And why do the doughnuts at sky enable 'respond to pings' by default, this is a security risk.

EPIC FAIL ... Ping Reply: RECEIVED (FAILED) � Your system REPLIED to our Ping (ICMP Echo) requests, making it visible on the Internet. Most personal firewalls can be configured to block, drop, and ignore such ping requests in order to better hide systems from hackers. This is highly recommended since "Ping" is among the oldest and most common methods used to locate systems prior to further exploitation.

Edited by deleted (Fri 10-Jun-11 10:56:59)

If you're on Vista or 7 the MTU should set automatically.

I think Sky set the option for responding to ping on by default to allow them to query to the router as to whether it is on-line or not.

Yeah win7, thx for info.

Will not allowing my router to respond to pings affect service?

In reply to a post by Tox_Laximus:

Yeah win7, thx for info.

Will not allowing my router to respond to pings affect service?

Things like TBB's ping test (BQM) will not work.

Been messing around with mtu, if you set to 1400 it stays at 1400, but setting to 1500 it goes to 1458.

I know a while back it used to be 1500 and you could set to 1500, there must of been a ms update to stop it going higher than 1458, which is probably a good thing.

After digging up my old posts I found I had quite a unstable connection with MTU on ROUTER 1458, MTU on PC 1500.

Respond to pings should be off by default really, firewall test ... https://www.grc.com/x/ne.dll?bh0bkyd2

In reply to a post by Tox_Laximus:

I know a while back it used to be 1500 and you could set to 1500, there must of been a ms update to stop it going higher than 1458, which is probably a good thing.

I use Windows Vista and there's definitely no problem having an MTU of 1500. I think it's unlikely Windows 7 is any different.

C:\>ping -f -l 1472 bbc.co.uk

Pinging bbc.co.uk [212.58.254.251] with 1472 bytes of data:
Reply from 212.58.254.251: bytes=1472 time=40ms TTL=248
Reply from 212.58.254.251: bytes=1472 time=39ms TTL=248
Reply from 212.58.254.251: bytes=1472 time=39ms TTL=248
Reply from 212.58.254.251: bytes=1472 time=39ms TTL=248

Ping statistics for 212.58.254.251:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 39ms, Maximum = 40ms, Average = 39ms

If your MTU is changing itself then I'd first check your security software.

On Windows Vista, Windows 7, and Mac OS X, there is not normally any reason to change the MTU as these operating systems "self adjust" as they monitor the path of the current connection.

If your router is at 1400 but your PC is at 1500 you're giving the router a lot of work to do in splitting every packet, which many routers don't have a very fast CPU so the effect is your connection seems "slow".

Being pingable means servers you connect to can ping your router to determine path-mtu; some mistaken security organisations (including Steve Gibson at GRC) seem to think that ignoring pings is a security feature. Nope; "hackers" / malicious intruders can still port scan you. (your router).

Ethernet runs best at 1500 and I think MER is a type of routed Ethernet so 1500 is correct.

If sky want to be able to ping their router, why not?

Dr TCP fixed the mtu, the problem was probably in the registry, and windows 7 does not set the mtu automatically.

As for letting your router respond to ping requests, when playing hide and seek is it best to answer if the seeker calls out, or is it better to keep quiet?

In reply to a post by BatBoy:

Ethernet runs best at 1500 and I think MER is a type of routed Ethernet so 1500 is correct.

Ethernet runs at any MTU. Yes if you have a single switch (or hub) segment, then 1500 is the biggest a regular network runs at. (Unless its a newer one with jumbo frames).

But on a WAN using lots of different networking technologies, the MTU can rise and fall, as a packet passes through switches and routers and/or firewalls.