Mult-Router L2TP LNS Configuration
From ImageStream Router Documentation
For load balancing and redundancy the LAC normally is configured with a list of LNS IPs. Often LACs in a certain region will be configured to send to a particular cluster of LNS IPs. The LAC will round-robin between the LNS routers automatically as new client PPP sessions are established. If an LNS goes down all PPP sessions on that LNS will terminate or eventually time out and re-establish on other active LNSs in the cluster. The LAC will cache the status of previous LNS connection attempts.
This example shows how to configure the router as part of a cluster of router acting as an LNS. This configuration uses Ospf to distribute routing information between a distribution router and between the routers in the cluster.
The L2TP configuration is very simple: for more information on LNS configuration see the following manual page.
! interface Loopback0 ip address 188.8.131.52 255.255.255.255 ! interface Tunnel0 description vlan1220 tunnel mode l2tp tunnel peer name default tunnel local name isnet tunnel key h18sJ98l tunnel virtual-template 1 ! interface Virtual-Template1 ip unnumbered Loopback0 peer default ip pool pool1 radius-server host 184.108.40.206 acct-port 1813 auth-port 1812 key password ppp authentication pap chap mtu 1500 ! ip local pool pool1 220.127.116.11 18.104.22.168 ip local pool pool1 22.214.171.124 126.96.36.199 ip name-server 188.8.131.52 ip name-server 184.108.40.206 !
For this example the telco would specify our local name as gbnet and our password as h18sJ98l. The telco also specified the use of VLAN 1220 and our IP range of 10.15.0.2 - 10.15.0.6 for our LNS cluster. Our telco also specifies a 1600 byte MTU on the GigE port to avoid IP fragmentation of large frames being tunneled.
# L2TP sessions come in to us on VLAN 1220 via Ethernet1. Bell uses a 1600 byte MTU on their GigE # interfaces to avoid IP fragmentation overhead when tunneling large frames. ! interface Ethernet1 no ip address speed 1000 duplex full mtu 1600 ! interface Ethernet1.1220 mtu 1600 description vlan1220 3AGAS ip address 10.15.0.2 255.255.255.248 !
The goal of the OSPF configuration is to export routing information to a traffic distribution router and between the other routers in the LNS cluster. In this example the routers are connected to the distribution router via Ethernet interface Ethernet0 with an ip address of 220.127.116.11/24. In the example below we use the same ip address ranges as the LNS example above.
! router ospf redistribute connected network 18.104.22.168/24 area 0.0.0.0 distribute-list PPP_OUT out connected ! access-list PPP_OUT permit 22.214.171.124/22 access-list PPP_OUT permit 126.96.36.199/22 access-list PPP_OUT deny any !