Hcip notes 12 days

8, Routing reflectors

Reflection rules of routing reflectors ：

1, When a route reflector learns a route from its client , Then he will reflect this routing information to all his customers and non customers

2, If the route reflector learns a route from its non customers , Then he will reflect this routing information to all his customers, but he cannot

because IBGP Horizontal segmentation is to prevent the generation of loops , The route reflector reflects the route and then breaks IBGP The horizontal division of , It may cause the appearance of the loop .

Originator ID --- O_ID --- When a routing message comes to the routing reflector , The reflector needs to reflect this route information , This attribute will be added to the routing information before reflection , The value of this attribute is the notifier of the reflector receiving this route information RID, after , Other routing reflectors receive a routing message if it contains O_ID, Then he will not change this attribute .

If in a AS among , There are multiple reflections , Then there must be multiple reflection clusters , Then each RR When reflecting the routing information, local clusters will be added to the cluster list attribute ID. When a device receives a reflected routing message , The cluster list attribute contains local clusters ID, You will no longer learn this route , To prevent the generation of loops .

[r3-bgp]peer 2.2.2.2 reflect-client --- Appoint R2 As a reflective customer , At the same time R3 Automatically become RR

9, The federal

The idea of the union is to put the same AS In the middle of IBGP The peer relationship is changed to EBGP Peer relationship , In this way to break IBGP The horizontal division of . This requires different IBGP Peers are divided into different members AS among , member AS Between the establishment of EBGP Peer relationship is a special EBGP Peer relationship , They only follow EBGP Transitivity of peers , From the perspective of the content of transmission , Still need to follow AS-BY-AS The rules , Because from a macro point of view , They are still in the same AS among .

The federal approach is also equivalent to breaking IBGP The horizontal division of , Loop problems may also occur , You need to consider anti ring . The anti ring method can be directly used for reference EBGP Horizontal segmentation , stay AS_PATH Add members to the attribute AS No. to prevent loopback . Be careful ： To distinguish members AS And normal AS, member AS The number will be enclosed in parentheses .

Configuration of federation ：

[r2]bgp 64512 --- Federate device startup

10,BGP The road selection principle

BGP The prerequisite for choosing a route --- Discard all unavailable routing information

1, optimization PV The route with the largest value

PV Value is Huawei's private attribute , It can be understood as weight , The greater the numerical , The higher the priority , And because he is the first principle in the road selection principles , therefore , This attribute is the most convenient attribute for routing on this device .--- This attribute can only take effect on this device , He can't pass it on to anyone BGP peers .

modify PV Affect the configuration of routing ：

Method 1 ： Global modification

Load sharing --- That is, let different traffic go on different lines , Share the pressure of a single line .

2, optimization LP The route with the largest attribute value

LP --- Local priority --- The default value is 100, The bigger the better . This property can be used in IBGP Between peers

3, The priority of self initiated routes is higher than that learned from peers , There are many ways to start your own , Their priority relationship is manual aggregation > Automatic aggregation >network>import

4, optimization AS_PATH Attribute the shortest route

AS_PATH Attributes in