I. Definition of redistribution
Route redistribution refers to the ability of border routers linked to different routing selection domains to exchange and advertise route selection information between different Autonomous Systems.
650) this. width = 650; "border =" 0 "alt =" "src =" http://www.bkjia.com/uploads/allimg/131227/025T54b2-0.gif "/>
II. We must understand the principles of redistribution. Otherwise, problems arising from redistribution cannot be solved)
1. A vro responsible for redistribution must have a route entry learned by the redistribution routing protocol or an interface under the redistribution routing protocol.
2. The route table entries of the routers responsible for redistribution remain unchanged Before and After redistribution.This principle is demonstrated through a classic redistribution experiment:
Tutorial topology:
650) this. width = 650; "border =" 0 "alt =" "src =" http://www.bkjia.com/uploads/allimg/131227/025T54620-1.gif "/>
Lab requirements: configure the interface addresses and routing protocols; repeat the routes by arrow); observe the route entries of Each router.
Before the experiment, let's imagine the results of the experiment: ps: just as I thought at the beginning, the result of the experiment is fading ~~~)
Possible result 1: R1 uses rip ----- "ospf", while ospf ---- "ospf", while that of ospf ------- "rip". Wow! A big loop! Infinite recursion, nesting... the last route table will crash!
Possible result 2: There is no result at all, because for example, R2 does not add this route when 2.2.2.2 goes back from a bend, because the local connection has a higher priority of 2.2.2.2; but R2 should be able to learn 3.3.3.3 of R3, because there is no local connection. This also applies to R3 and R4.
Well, the above two ideas are not without reason, but they are all wrong! The key is not to understand the principles of redistribution.
Experiment Configuration:
Step 1: Configure each interface address and route protocol interface)R1:
Router VPN 100
Network 14.1.1.1 0.0.0.0
Auto-summary
!
Router ospf 1
Log-adjacency-changes
Network 13.1.1.1 0.0.0.0 area 0
!
Router rip
Version 2
Network 12.0.0.0
No auto-summary R2:
Router rip
Version 2
Network 0.0.0.0
No auto-summary R3: router ospf 1
Log-adjacency-changes
Network 0.0.0.0 255.255.255.255 area 0 R4: router VPN 100
Network 0.0.0.0
No auto-summary
Step 2: Configure route redistribution on R1:
Router
Rip
Version 2
Metric needs to be specified for redistribute Kerberos 100 metric 1 Distance vector protocol redistribution)! Router
Ospf 1
Redistribute rip subnets does not have the keyword subnet, so it will not be able to re-distribute the classless Network)! Router
VPN 100
Redistribute ospf 1 metric 10000 100 255 1 1500
Specify metric for distance vector protocol redistribution
)
Implementation symptom:
After step 1 is completed, the route table of R1 is not re-distributed ):
R1 # sh ip route rip
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
R1 # sh ip route ospf
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 13.1.1.3, 00:06:15, Serial0/1
R1 # sh ip route VPN
4.0.0.0/32 is subnetted, 1 subnets
D 4.4.4.4 [90/409600] via 14.1.1.4, 00:06:36, FastEthernet0/0
The route table of each vro after Step 2 is completed:R1:
R1 # sh ip route rip
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 12.1.1.2, 00:00:09, Serial0/0
R1 # sh ip route ospf
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 13.1.1.3, 00:06:15, Serial0/1
R1 # sh ip route VPN
4.0.0.0/32 is subnetted, 1 subnets
D 4.4.4.4 [90/409600] via 14.1.1.4, 00:06:36, FastEthernet0/0
The above demonstrates Principle 2:"
The route table entries of the routers responsible for redistribution do not change before and after redistribution"
R2:
R2 # sh ip route rip
4.0.0.0/32 is subnetted, 1 subnets
R 4.4.4.4 [120/1] via 12.1.1.1, 00:00:05, Serial0/0----------------------------- The route entry is learned by using iver1.
14.0.0.0/24 is subnetted, 1 subnets
R 14.1.1.0 [120/1] via 12.1.1.1, 00:00:05, Serial0/0 ------------------------------ this interface is in the ospf process of R1
-------- Introduction from VPN ------------------------------------------
Ps: No 3.3.3.3)
R3:
R3 # sh ip route ospf
2.0.0.0/32 is subnetted, 1 subnets
O E2 2.2.2.2 [110/20] via 13.1.1.1, 00:05:46, Serial0/1----------------------------- The route entry is learned by rip on R1.
12.0.0.0/24 is subnetted, 1 subnets
O E2 12.1.1.0 [110/20] via 13.1.1.1, 00:05:47, Serial0/1
------------------------------ The interface is in the rip process of R1
---------------- Introduction from rip ------------------------------------
R4:
R4 # sh ip route VPN
3.0.0.0/32 is subnetted, 1 subnets
D ex 3.3.3.3 [170/307200] via 14.1.1.1, 00:06:26, FastEthernet0/0----------------------------- R1 learns this route using ospf
13.0.0.0/24 is subnetted, 1 subnets
D ex 13.1.1.0 [170/307200] via 14.1.1.1, 00:06:26, FastEthernet0/0 --------------------- this interface is in the ospf process of R1
------------------- Introduction from ospf --------------------------------------------
It can be seen that entries not in the corresponding routing process cannot be redistributed, which indicates that our previous assumptions are incorrect!
The above demonstrates the first principle:
1. A vro responsible for redistribution must have a route entry learned by the redistribution routing protocol or an interface under the redistribution routing protocol.
Only by correctly understanding the principles of Route redistribution can we correctly handle routing loops and routing problems caused by route redistribution in the future, and discard such problems: incorrect conclusion that "the route to be redistributed cannot be re-distributed !....
PS: I think the principle is "whether or not the re-distribution is performed on the re-distribution router, the re-distribution route must be learned in the form of the re-distribution routing protocol ." It may be easier to understand.| \/This is done
Dual-point bidirectional redistributionAt the same time, only one VBR can be redistributed successfully. The most important factor is the most critical factor !!
This article is from the "shark" blog and will not be reposted!
