if I have a router with 1 serial and and ethernet both going to the same place, How would I get it to route via the ethernet and if that goes down use the serial, can I use eigrp or do I need to use statics ?
first thing would be using simple gre tunnels built over the ethernet and serial links.
route the traffic accordingly using simple static routes one with admin distance and the other one which will be your primary route without any admin distance.
Also keepalives on the gre tunnels should be taken care for auto fall over whenever theres some probs with the ethernet link.
second thing would be something inline with the object tracking which i would suggest to check out using this link..
If you have that scenario then you can use floating static route to back up the primary route.
ip route 0.0.0.0 0.0.0.0 eth0
ip route 0.0.0.0 0.0.0.0 se0 200
you cna also use either of the interface back for other. do the following:
int e 0
backup interface se 0
You can also do the static route load-balancing using both the routes.
ip route 0.0.0.0 0.0.0.0 eth0
ip route 0.0.0.0 0.0.0.0 se0
If you have EIGRP running already then it will take care of it. If you have an equal path cost then it will do the auto load-balancing on the link, whihc will not likely to be the case as bandwitdh will be diff for both the links. You can configure EIGRP to to do uequal cost path load-balancing using Varience command with the feasibility condition satisfied.
i.e AD < FD
What is GRE, What does it stand for, and why would I need to create GRE tunnels ?
also if I use the backup interface command, does it shut the interface down until needed ?
GRE stands for generic routing encapsulation. Tunneling protocol developed by Cisco that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to Cisco routers at remote points over an IP internetwork.
If you use the backup interface command it will put the interface in standby mode with lie protocol down.
So if you do " show int se 0", it will show as:
interface se0 in standby mode, line protocol down
Ethernet interfaces wont go down untill unless if the cable is physically removed from the port or the other end where its connecting goes off.
If theres some probs with the Laser or RF link ethernet port will still remain on and that will blackhole all your traffic.
coz untill unless the protocol goes down on the interface the active static route wont be removed from the routing table and it will still remain there though you dont have any connectivity to the remote location.
GRE is nothing but just creating some kinda logical link over your physical connectivity either your ethernet or serial link which is the case here.
So once the remote GRE endpoint(destination) is unreachable the route will be removed and the traffic will flow via your secondary link.
once the main connectivity comes up so as your primary gre tunnel.
its nothing but adding extra ip header which is termed as "encapsulation" over the original payload.
We have got some links in our live production network running with GRE where we got either RF or Laser links which has ethernet outputs..
Varience command is used under the " router EIGRP command ". You need to change the bandwitdh or delay only in case of making a route favourable and stisfy the feasibility condition.
With back-up interface command, you need to put 2 static routes one whihc will be pointing to the main interface and another floating static route poinintg to the backup interface.
do you need to put a different cost on the route to the serial or put them the same ? and why use the interfac backup command, wouldnt static routes 1 with a lower cost work ?
There will be different metric for both the links. If your link doesnot satisfy the feasibility condition, then it will not be used for load balancing with EIGRP. You need to change the cost only to make the route to satisfy the feasibility condition.
For example if EIGRP gets a metric of 200 via serial interface and 150 via ethernet. By-default varience is 1 and the feasible distenace i.e best metric is 200x1=200.
Your Eth int has a metric 150 which will not be used for load-balancing as 150>200 as they both are not the equal path cost.
Now if you configure Varience as 2
route eigrp 1
So now the best metric will be multiply by 2 i.e 200x2=400 i.e now eth interface with vlaue 150 will be used for load-balancing which satisfy the feasilbilty condition 150<200.
There is no need to use the bacnkup interface command in case of static routes, its is only used in case of dial-up connection where a simple hello or keep-alive traffic can triger the call. Only one static route with lower cost work out for you..
by using the backup interface command, do you need to put static routes to both interfaces in or just put a route to the ethernet and if that goes down, it will route it out of the serial automatically
Yes you would need it to route it to both interfaces. Backup interface will kick in only when primary is down. But Serial backing up ethernet is better if you have a routing protocol or SAA tracking