my cisco router has 1500 for int gi8 (connected via cable modem to ISP):
int gi8 has default MTU 1500:
gate(config-if)#do sh ip int gi 8 | i MTU
MTU is 1500 bytes
gate(config-if)#
openwrt router from other side of ipsec VPN tunnel has default MTU as well:
root@a81m5:/home/sam# ip link sh
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:44 brd ff:ff:ff:ff:ff:ff
4: wlan1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
5: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
6: eth0.10@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
7: br-voice: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
8: eth0.13@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-voice state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:45 brd ff:ff:ff:ff:ff:ff
9: eth0.2@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether e8:de:27:ff:9f:46 brd ff:ff:ff:ff:ff:ff
root@a81m5:/home/sam#
Bellow relives me suspect I have MTU issue:
Whenever I login from LAN2 linux to LAN1 openwrt via ipsectunnel I'm able to read small files (/etc/hosts) but big one (etc/config/firewall) freezes:
[sam@st1 open-wrt]$ ssh 192.168.173.1 -p52407
sam@192.168.173.1's password:
BusyBox v1.28.4 () built-in shell (ash)
----------------------------------
OpenWrt 18.06.7, r7976-ca47026b7d
----------------------------------
sam@a81m5:~$ sudo ash
Password:
BusyBox v1.28.4 () built-in shell (ash)
root@a81m5:/home/sam#
root@a81m5:/home/sam#
root@a81m5:/home/sam#
root@a81m5:/home/sam# cat /etc/hosts
127.0.0.1 localhost
192.168.172.2 main.st1.org main
192.168.172.1 gate.st1.org gate
192.168.172.3 db4.st1.org db4
192.168.172.9 ns3.st1.org ns3
192.168.172.9 ap.sit1.org ap
192.168.172.4 ns2.st1.org ns2
192.168.172.38 spa.st1.org spa
192.168.174.34 spa-c7.st1.org spa-c7
192.168.174.4 ltop-c7.st1.org ltop-c7
#::1 localhost ip6-localhost ip6-loopback
#ff02::1 ip6-allnodes
#ff02::2 ip6-allrouters
root@a81m5:/home/sam#
root@a81m5:/home/sam#
root@a81m5:/home/sam#
root@a81m5:/home/sam# cat /etc/config/firewall
**-= couple minutes freeze here ..... =-**
packet_write_wait: Connection to 192.168.173.1 port 52407: Broken pipe
I think I need to setup proper MTU for openwrt interfaces but completely got in stack w/ my experiments.
I've fount icmp packet size 1410 fit the tunnel:
[sam@st15 open-wrt]$ ping -M do -s 1411 192.168.173.1 -c2
PING 192.168.173.1 (192.168.173.1) 1411(1439) bytes of data.
--- 192.168.173.1 ping statistics ---
2 packets transmitted, 0 received, 100% packet loss, time 1001ms
[sam@st15 open-wrt]$ ping -M do -s 1410 192.168.173.1 -c2
PING 192.168.173.1 (192.168.173.1) 1410(1438) bytes of data.
1418 bytes from 192.168.173.1: icmp_seq=1 ttl=63 time=18.0 ms
1418 bytes from 192.168.173.1: icmp_seq=2 ttl=63 time=19.1 ms
--- 192.168.173.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 17.951/18.526/19.101/0.575 ms
[sam@st15 open-wrt]$
but where I have to setup MTU 1410 at openwrt router (a81m5) behind the tunnel? interfaces eth.0,.2 (wan) eth0, eth0.10, eth0.13, br-lan, br-wan?