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MTU Settings for VPNs - RV042/RV082

Discussion in 'Cisco Small Business Routers and VPN Solutions' started by Toxic, Jul 11, 2006.

  1. Toxic

    Toxic Administrator Staff Member

    I am just curious as to what MTU is being set here when talking about MTU values and VPN gateway setups on the RV042 and RV082 routers.

    If you set the MTU setting in the firewall page, this effectively sets the packet size permitted for network transmission across Both WAN/LANs? yes?

    My RV042 set with MTU 1500 (firewall manually set as 1500)

    now lets look at the interfaces:

    ipsec0 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:xx
    inet addr:xx.xx.95.251 Mask:255.255.252.0
    UP NOTRAILERS RUNNING MULTICAST MTU:1440 Metric:1
    RX packets:0 errors:0 dropped:0 overruns:0 frame:0
    TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:10
    RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

    ixp0 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:xx
    inet addr:192.168.x.x Bcast:192.168.x.xxx Mask:255.255.255.0
    UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:144761 errors:0 dropped:0 overruns:0 frame:0
    TX packets:200564 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:100
    RX bytes:32531332 (31.0 Mb) TX bytes:159846246 (152.4 Mb)

    ixp1 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:xx
    inet addr:xx.xx.xx.xxx Bcast:xx.xx.xx.xxx Mask:255.255.252.0
    UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
    RX packets:173610 errors:0 dropped:0 overruns:0 frame:0
    TX packets:137916 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:100
    RX bytes:150885724 (143.8 Mb) TX bytes:31287832 (29.8 Mb)

    lo Link encap:Local Loopback
    inet addr:127.0.0.1 Mask:255.0.0.0
    UP LOOPBACK NOTRAILERS RUNNING MULTICAST MTU:16436 Metric:1
    RX packets:209 errors:0 dropped:0 overruns:0 frame:0
    TX packets:209 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:0
    RX bytes:12384 (12.0 kb) TX bytes:12384 (12.0 kb)

    NOW we have MTU for ixp0 (LAN) and ixp1 (WAN) both on 1500

    but whats this..... ipsec0 MTU 1440

    now. if this is the case surely ipsec0 is for VPN connections, and no matter what MTU you are setting in firewall the MTU is set by ipsec0 surely?

    ie:

    ifconfig ipsec0 mtu 1400

    ipsec0 Link encap:Ethernet HWaddr 00:xx:xx:xx:xx:xx
    inet addr:xx.xx.xx.xxx Mask:255.255.252.0
    UP NOTRAILERS RUNNING MULTICAST MTU:1400 Metric:1
    RX packets:0 errors:0 dropped:0 overruns:0 frame:0
    TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
    collisions:0 txqueuelen:10
    RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
     
  2. OpticalMan

    OpticalMan LI Guru Member

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