On 01/04/2015 03:30 PM, James Knott wrote:
On 01/04/2015 01:59 PM, Kevin Cozens wrote:
On 15-01-04 12:55 PM, James Knott wrote:
One thing I noticed recently was that my firewall, running Linux, was getting a MTU of 576 bytes, instead of the normal 1500 bytes. This was being set by the Rogers DHCP server (option 26). [snip] I have advised Rogers of this and the person I was speaking to agreed it should be 1500. Let's see if they fix it. I am on Rogers and just checked my MTU setting after reading James' email. The ifconfig output reports an MTU of 1500. I didn't change any settings for DHCP. Rogers may have already fixed the problem.
I just tried some more testing with my notebook computer. It uses the KDE network manager and appears to ignore the DHCP MTU value. However, I can only ping with up to 1472 bytes when connected to the cable modem. I get the same when I tether to my smart phone (Rogers), but get the full 1500 to a local computer on my network. I do not use DHCP option 26 on my DHCP server. It also doesn't appear to be used when tethered to my smart phone.
--- GTALUG Talk Mailing List - talk@gtalug.org http://gtalug.org/mailman/listinfo/talk $ ping -s 1500 acm.org PING acm.org (64.238.147.76) 1500(1528) bytes of data. 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=1 ttl=49 time=42.5 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=2 ttl=49 time=44.1 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=3 ttl=49 time=44.5 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=4 ttl=49 time=44.2 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=5 ttl=49 time=52.9 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=6 ttl=49 time=44.1 ms ^C --- acm.org ping statistics --- 6 packets transmitted, 6 received, 0% packet loss, time 5007ms rtt min/avg/max/mdev = 42.576/45.430/52.995/3.445 ms
From a different rogers subnet, I get a default of 56, successes with 1500-byte pings to the router and to the outside world, but failures internally talking to rogers DNS servers First, the dns server: $ cat /etc/resolv.conf # Generated by NetworkManager nameserver 64.71.255.204 nameserver 64.71.255.198 $ ping -s 1500 64.71.255.204 PING 64.71.255.204 (64.71.255.204) 1500(1528) bytes of data. ^C --- 64.71.255.204 ping statistics --- 19 packets transmitted, 0 received, 100% packet loss, time 17999ms $ ping 64.71.255.204 PING 64.71.255.204 (64.71.255.204) 56(84) bytes of data. 64 bytes from 64.71.255.204: icmp_seq=1 ttl=58 time=7.63 ms 64 bytes from 64.71.255.204: icmp_seq=2 ttl=58 time=7.35 ms ^C --- 64.71.255.204 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1002ms rtt min/avg/max/mdev = 7.350/7.492/7.635/0.166 ms Second, ACM.org $ ping -s 1500 acm.org PING acm.org (64.238.147.76) 1500(1528) bytes of data. 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=1 ttl=49 time=42.5 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=2 ttl=49 time=44.1 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=3 ttl=49 time=44.5 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=4 ttl=49 time=44.2 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=5 ttl=49 time=52.9 ms 1508 bytes from ACMWEB16.acm.org (64.238.147.76): icmp_seq=6 ttl=49 time=44.1 ms ^C --- acm.org ping statistics --- 6 packets transmitted, 6 received, 0% packet loss, time 5007ms rtt min/avg/max/mdev = 42.576/45.430/52.995/3.445 ms --dave -- David Collier-Brown, | Always do right. This will gratify System Programmer and Author | some people and astonish the rest davecb@spamcop.net | -- Mark Twain