What would the router use as metrics when having different routing protocol in the routing table?
A. Prefix length
What would the router use as metrics when having different routing protocol in the routing table?
What would the router use as metrics when having different routing protocol in the routing table?
A. Prefix length
Prefix Lengths
Let’s look at another scenario to see how the router handles another common situation: varying prefix lengths. Assume, again, that a router has four routing processes running on it, and each process has received these routes:
EIGRP (internal): 192.168.32.0/26
RIP: 192.168.32.0/24
OSPF: 192.168.32.0/19
Which of these routes will be installed in the routing table? Since EIGRP internal routes have the best administrative distance, it’s tempting to assume the first one will be installed. However, since each of these routes has a different prefix length (subnet mask), they’re considered different destinations, and they will all be installed in the routing table.
Let’s see how the forwarding engine uses the information from the routing table to make forwarding decisions.
Making Forwarding Decisions
Let’s look at the three routes we just installed in the routing table, and see how they look on the router.
router# show ip route
….
D 192.168.32.0/26 [90/25789217] via 10.1.1.1
R 192.168.32.0/24 [120/4] via 10.1.1.2
O 192.168.32.0/19 [110/229840] via 10.1.1.3
….
If a packet arrives on a router interface destined for 192.168.32.1, which route would the router choose? It depends on the prefix length, or the number of bits set in the subnet mask. Longer prefixes are always preferred over shorter ones when forwarding a packet.
In this case, a packet destined to 192.168.32.1 is directed toward 10.1.1.1, because 192.168.32.1 falls within the 192.168.32.0/26 network (192.168.32.0 to 192.168.32.63). It also falls within the other two routes available, but the 192.168.32.0/26 has the longest prefix within the routing table (26 bits verses 24 or 19 bits).
Likewise, if a packet destined for 192.168.32.100 arrives on one of the router’s interfaces, it’s forwarded to 10.1.1.2, because 192.168.32.100 doesn’t fall within 192.168.32.0/26 (192.168.32.0 through 192.168.32.63), but it does fall within the 192.168.32.0/24 destination (192.168.32.0 through 192.168.32.255). Again, it also falls into the range covered by 192.168.32.0/19, but 192.168.32.0/24 has a longer prefix length.
i kinda agree on the AD first then the most precise route depending on prefix/netmask, at least on Cisco equipment
static route will be used before dynamic routing afaik, because Cisco trust more Admins than protocols
if anyone has better arguments, i would be happy to hear it
I agree
Routes are already in the routing table. So the most specific Prefix lenght is taken.
I think the right answer is administrative distance
I believe this should be the AD (Administrative Distance)