RIB, FIB, CEF, adjacency tables

dppagc

Correct me if I am wrong:

RIB-> possible routing routes
FIB -> parsed from RIB
CEF -> good info from FIB
adjacency tables ???

EdTheLad

The RIB hold all known routes learned from the various routing protocols including static or connected. These routes appear as learned i.e. with the next-hop that was provided by the routing protocol which means the route could be recursive.
The FIB holds has all routes from the RIB but it holds the results of the recursive lookup against destination ip address and points to the exit interface.
The adjacency table holds the L2 info for all directly connected neighbors i.e. the mac address of directly connected device.
CEF uses both the FIB and ADJ table to create header that can be pushed onto frames quickly as they get forwarding through the router. Rather than the router performing a recursive lookup, finding the exit interface, checking the arp cache of exit interface for remote mac etc, packet arrives for destination and gets the cef destination header added.

james43026

RIB = Routing table.
FIB = a tree like structure built for hardware (not the CPU) to parse through to match IP addresses, and determine next hop address and exit interface.
Adjacency table = information that the FIB points to in order to determine next hop MAC info
CEF = FIB + Adjacency table

linuxabuser

When you run show ip cef you'll see routes from all VRFs. A show ip route​ is per-vrf.

fredrikjj

linuxabuser wrote: »

When you run show ip cef you'll see routes from all VRFs. A show ip route​ is per-vrf.

That's not true. This is a router that I'm working with at the moment:

R2#show ip cef
Prefix               Next Hop             Interface
0.0.0.0/0            no route
0.0.0.0/8            drop
0.0.0.0/32           receive              
10.1.23.0/24         attached             GigabitEthernet0/2
10.1.23.0/32         receive              GigabitEthernet0/2
10.1.23.2/32         receive              GigabitEthernet0/2
10.1.23.3/32         attached             GigabitEthernet0/2
10.1.23.255/32       receive              GigabitEthernet0/2
10.1.24.0/24         attached             GigabitEthernet0/3
10.1.24.0/32         receive              GigabitEthernet0/3
10.1.24.2/32         receive              GigabitEthernet0/3
10.1.24.4/32         attached             GigabitEthernet0/3
10.1.24.255/32       receive              GigabitEthernet0/3
10.1.35.0/24         10.1.23.3            GigabitEthernet0/2
10.1.45.0/24         10.1.24.4            GigabitEthernet0/3
127.0.0.0/8          drop
192.168.1.2/32       receive              Loopback0
192.168.1.3/32       10.1.23.3            GigabitEthernet0/2
192.168.1.4/32       10.1.24.4            GigabitEthernet0/3
192.168.1.5/32       192.168.1.5          Tunnel3
                     192.168.1.5          Tunnel4
Prefix               Next Hop             Interface
224.0.0.0/4          drop
224.0.0.0/24         receive              
240.0.0.0/4          drop
255.255.255.255/32   receive              
R2#show ip cef vrf CUST_A
Prefix               Next Hop             Interface
0.0.0.0/0            no route
0.0.0.0/8            drop
0.0.0.0/32           receive              
10.1.12.0/24         attached             GigabitEthernet0/1
10.1.12.0/32         receive              GigabitEthernet0/1
10.1.12.1/32         attached             GigabitEthernet0/1
10.1.12.2/32         receive              GigabitEthernet0/1
10.1.12.255/32       receive              GigabitEthernet0/1
127.0.0.0/8          drop
192.168.1.1/32       10.1.12.1            GigabitEthernet0/1
192.168.1.6/32       192.168.1.5          Tunnel3
                     192.168.1.5          Tunnel4
224.0.0.0/4          drop
224.0.0.0/24         receive              
240.0.0.0/4          drop
255.255.255.255/32   receive              

As you can see, only the global table is shown with show ip cef and you need to specify the VRF if you want to show that information.

linuxabuser

I'll be damned. Learn something every day. I even looked at a lab router I have before I posted, but I didn't look carefully enough.