Data communication foundation - route republication

Route republication

• In some networks , There may be many routing protocols , Each routing protocol has different understanding and processing of routing information , So initially , Routing information is isolated between different routing protocols .

• Route republication （Route redistribution） Also known as route Introduction （Route importation）, It refers to the operation of publishing routing information from one routing protocol to another .

• Deploy route republishing in the network , The routing information can be transferred between various routing protocols , Thus, the data of the whole network can be interconnected .

RIP And OSPF There are two different routing protocols , The routing information of each other will not operate mutually by default , therefore R1 Can't learn OSPF Within the domain 192.168.3.0/24 And 192.168.4.0/24 route , Empathy R3 Can't learn RIP Within the domain 192.168.1.0/24 And 192.168.2.0/24 route .

Relevant points ：

• Route republishing , It is completed on the border device of the routing domain , Introduce routing information from one routing protocol to another .

• Transfer the routing information from the routing protocol A Introduced into the routing protocol B, It is in the routing protocol B Complete relevant configurations in the configuration view of .

• Route republication is directional , Transfer the routing information from the routing protocol A Introduced into the routing protocol B, Then the routing protocol B Can be informed A Routing information in , But at this time ,A I don't know yet B Routing information in the routing protocol , Unless you configure B-to-A Route republication for .

• Only routes that exist in the routing table can be successfully republished .

matters needing attention ：

• Routing priority

• Beware of route recharge

• Control of routing metrics

• Control of route convergence time （ Different routing protocols have different convergence speeds ）

Routing priority

R2 take R1 Notified 1.1.1.1/32 Republish to ospf domain , Give Way ospf All routers in the domain learn . in the meantime ,R3 It will be caused by the problem of routing priority Suboptimal path .

• OSPF The routing priority of is better than IBGP

• R3 Generate suboptimal paths , Go to 1.1.1.1/32 Data flow R4->R2->R1 This path .

• If R3 Deployed two-way route republishing , It will lead to routing 1.1.1.1/32 Backflow recirculation BGP

Routing protocol or routing type	The priority of the corresponding route
DIRECT	0
OSPF	10
IS-IS	15
STATIC	60
RIP	100
OSPF ASE	150
OSPF NSSA	150
IBGP	255
EBGP	255

One way is , stay R3 Modify the routing priority on , in the light of 1.1.1.1/32 The routing , take IBGP The priority of routing is adjusted better .

Another alternative is , stay R2 on BGP To OSPF When the route of is republished , Publish into OSPF The corresponding routing settings tag value , Later on R3 For this tag Value to further deploy route filtering 、 Adjust priorities 、 Route strategy based on republication, etc .

measurements

• OSPF The routing metric of is based on the path cost , It is related to the bandwidth of the interface ;

• RIP The routing metric of is based on hops ;

• Different routing protocols have different definitions and understandings of routing metrics , When deploying route republishing between routing protocols , How to define the metrics of the introduced route ？ How many ？

Method 1 , You can perform the action of republishing , Manually formulate the republished cost value .

Method 2 , Take the default action , That is, the seed metric used when republishing between routing protocols . The so-called seed measure , It refers to when a route is republished from an external routing protocol to this routing protocol , The default used cost value .

Basic configuration

RIP And OSPF Introduce each other

[R2] ospf 1
[R2-ospf-1] import-route ?
  bgp     	Border Gateway Protocol (BGP) routes
  direct  	Connected routes
  isis   	Intermediate System to Intermediate System (IS-IS) routes
  limit   	Limit the number of routes imported into OSPF
  ospf    	Open Shortest Path First (OSPF) routes
  rip     	Routing Information Protocol (RIP) routes
  static  	Static routes
  unr     	User Network Routes

[R2] rip
[R2-rip-1] import-route ospf 1 [cost x] 
#  If you don't specify cost, Then the route is republished into RIP after cost=1

[R2] ospf 1
[R2-ospf-1] import-route rip 
#  If you don't specify cost, Then the route is republished into OSPF after cost=1,type by E2, Can relate to cost And type Keyword modification cost And external routing metric-type.

Introduce direct routing to OSPF

[R3] ospf 1
[R3-ospf-1] import-route direct 
#  If you don't specify cost, Then the route is republished into OSPF after cost=1,type by E2, Can relate to cost And type Keyword modification cost And external routing metric-type.
#  Use direct keyword , Then all active local direct routes will be injected into OSPF.

Introduce static routing to OSPF

[R2] ip route-static 11.11.11.0 24 192.168.12.1
[R2] ospf 1
[R2-ospf-1] import-route static
#  If you don't specify cost, Then the route is republished into OSPF after cost=1,type by E2, Can keep up with cost And type Keyword modification cost And external routing metric-type.
#  Use static keyword , All active static routes in the routing table will be injected into OSPF.