2022-07-19 advanced network engineering (XX) BGP route optimization, route optimization analysis one by one

BGP Route optimization

When there are multiple routes to the same destination network segment ,BGP Route optimization is carried out in the following order

01 optimization Preferred-Value The attribute value is the largest The routing .

02 optimization Local_Preference The attribute value is the largest The routing .

03 Locally originated BGP Routing is better than the routing learned from other peers , Local origin priority ： optimization Manual aggregation > Automatic aggregation >network>import> What we learned from the equivalent .

04 optimization AS_Path The attribute value is the shortest The routing .

05 optimization Origin Attribute optimal routing .Origin The attribute value ranges from The high to low arrangement is ：IGP、EGP And Incomplete.

06 optimization MED The attribute value is the smallest The routing .

07 Preferably from EBGP Peer to peer routing （EBGP Routing priority is higher than IBGP route ）.

08 optimization To Next_Hop Of IGP The smallest measure The routing .

09 optimization Cluster_List The shortest The routing .

10 optimization Router ID（Orginator_ID） Smallest equipment Advertised routing .

11 optimization Minimum IP Peer notification of address The routing .

The above rules are arranged in order ,BGP When routing optimization , Start with the first rule , If you cannot make a judgment according to the first rule , For example, routed Preferred-Value Same property value , Then continue to execute the next rule , If according to the current rules ,BGP Can decide the best route , No further execution . Be similar to ACL Matching rules .

BGP Route optimization is analyzed one by one

The topology

see BGP Detailed routing , You can check the reasons for not being preferred

<R7>display bgp routing-table 11.11.11.11

 BGP local router ID : 7.7.7.7
 Local AS number : 200
 Paths:   2 available, 1 best, 1 select
 BGP routing table entry information of 11.11.11.11/32:
 From: 5.5.5.5 (5.5.5.5)
 Route Duration: 00h06m10s  
 Relay IP Nexthop: 20.2.0.5
 Relay IP Out-Interface: GigabitEthernet0/0/0
 Original nexthop: 5.5.5.5
 Qos information : 0x0
 AS-path 100, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, bes
t, select, active, pre 255, IGP cost 1
 Not advertised to any peer yet

 BGP routing table entry information of 11.11.11.11/32:
 From: 6.6.6.6 (6.6.6.6)
 Route Duration: 00h06m25s  
 Relay IP Nexthop: 20.3.0.6
 Relay IP Out-Interface: GigabitEthernet0/0/1
 Original nexthop: 6.6.6.6
 Qos information : 0x0
 AS-path 100, origin igp, localpref 100, pref-val 0, valid, internal, pre 255, I
GP cost 1, not preferred for router ID
 Not advertised to any peer yet

analysis ： among , The second route is indicated at the bottom “not preferred for router ID”, The reason why this route is not preferred is Router ID The larger .

multiple BGP Routing load balancing （ Affect this machine ）

[R7-bgp]maximum load-balancing ibgp ?
  INTEGER<1-8>  Specify maximum equal cost routes

01 optimization Preferred-Value The attribute value is the largest The routing （ Unique attributes of Huawei equipment ）

Modify attribute method ：

1 Use preferred-value Command to change （ Modify on this machine , Routing optimization that affects itself ）

[R7]bgp 200
[R7-bgp]peer 6.6.6.6 preferred-value 100

View modified results

<R7>display bgp routing-table 

 BGP Local router ID is 7.7.7.7 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete


 Total Number of Routes: 11
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  11.11.11.11/32     6.6.6.6                    100        100    100i
 * i                     5.5.5.5         0          100        0      100i
 *>i  22.22.22.22/32     6.6.6.6         0          100        100    100i
 * i                     5.5.5.5                    100        0      100i
 *>i  33.33.33.33/32     6.6.6.6                    100        100    100i
 * i                     5.5.5.5                    100        0      100i
 *>i  44.44.44.44/32     6.6.6.6                    100        100    100i
 * i                     5.5.5.5                    100        0      100i
 *>i  55.55.55.55/32     5.5.5.5         0          100        0      i
 *>i  66.66.66.66/32     6.6.6.6         0          100        100    i
 *>   77.77.77.77/32     0.0.0.0         0                     0      i

analysis ：PrefVal Routes with large fields , Be preferred . modify preferred-value The feature of is that all the next hops are 6.6.6.6 All routes are optimized , Belong to right overall situation Make changes .

2 Use the routing policy to modify （ Modify on this machine , Routing optimization that affects itself ）

[R7]acl 2000
[R7-acl-basic-2000]rule 5 permit source 11.11.11.11 0

[R7]route-policy 1 permit node 10
[R7-route-policy]if-match acl 2000
[R7-route-policy]apply preferred-value 200

[R7]bgp 200
[R7-bgp]peer 5.5.5.5 route-policy 1 import 

View modified results

<R7>display bgp routing-table 

 BGP Local router ID is 7.7.7.7 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete


 Total Number of Routes: 7
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  11.11.11.11/32     5.5.5.5         0          100        200    100i
 * i                     6.6.6.6                    100        100    100i
 *>i  22.22.22.22/32     6.6.6.6         0          100        100    100i
 *>i  33.33.33.33/32     6.6.6.6                    100        100    100i
 *>i  44.44.44.44/32     6.6.6.6                    100        100    100i
 *>i  66.66.66.66/32     6.6.6.6         0          100        100    i
 *>   77.77.77.77/32     0.0.0.0         0                     0      i

analysis ： Adopt the method of policy routing to modify , You can modify a specified route entry , Relative to 1 Medium method , More accurate .

02 optimization Local_Preference The attribute value is the largest The routing .

The local priority attribute will be in AS Internal delivery , Will not be passed on to others AS. The default value 100.

Modify attribute method ：

1 Modify the default local priority （ stay AS Inner boundary routing modifier , influence AS Other internal routers ）

[R5]bgp 200
[R5-bgp]default local-preference 200

[R6]bgp 200
[R6-bgp]default local-preference 200

View modified results

<R7>dis bgp routing-table

 BGP Local router ID is 7.7.7.7 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete


 Total Number of Routes: 11
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  11.11.11.11/32     5.5.5.5         0          200        0      100i
 * i                     6.6.6.6                    200        0      100i
 *>i  22.22.22.22/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6         0          200        0      100i
 *>i  33.33.33.33/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6                    200        0      100i
 *>i  44.44.44.44/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6                    200        0      100i
 *>i  55.55.55.55/32     5.5.5.5         0          200        0      i
 *>i  66.66.66.66/32     6.6.6.6         0          200        0      i
 *>   77.77.77.77/32     0.0.0.0         0                     0      i

analysis ： all LocPrf The field values change to 200, Belong to right overall situation Make changes .

2  Use the routing policy to modify （ stay AS Inner boundary routing modifier , influence AS Other internal routers ）

[R5]acl 2000
[R5-acl-basic-2000]rule 5 permit source 11.11.11.11 0

[R5]route-policy 1 permit node 10
[R5-route-policy]if-match acl 2000
[R5-route-policy]apply local-preference 300
[R5]route-policy 1 permit node 20

[R5]bgp 200
[R5-bgp]peer 1.1.1.1 route-policy 1 import

View the modification results

<R7>display bgp routing-table

 BGP Local router ID is 7.7.7.7 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete


 Total Number of Routes: 10
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  11.11.11.11/32     5.5.5.5         0          300        0      100i
 *>i  22.22.22.22/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6         0          200        0      100i
 *>i  33.33.33.33/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6                    200        0      100i
 *>i  44.44.44.44/32     5.5.5.5                    200        0      100i
 * i                     6.6.6.6                    200        0      100i
 *>i  55.55.55.55/32     5.5.5.5         0          200        0      i
 *>i  66.66.66.66/32     6.6.6.6         0          200        0      i
 *>   77.77.77.77/32     0.0.0.0         0                     0      i

analysis ： Adopt the method of policy routing to modify , You can modify a specified route entry , Relative to 1 Medium method , More accurate .

03 Locally originated BGP Routing is better than the routing learned from other peers , Local origin priority ： optimization Manual aggregation > Automatic aggregation >network>import> What we learned from the equivalent

04 optimization AS_Path The attribute value is the shortest The routing

See

2022-07-15 Advanced network engineering （ nineteen ）BGP- State machine 、 The principle of interaction between peers 、 Factors that affect the establishment of peer relationships 、 Peer surface 、 Routing table 、 Detailed routing table 、 Routing properties _ Goose blog -CSDN Blog

05 optimization Origin Attribute optimal routing .Origin The attribute value ranges from The high to low arrangement is ：IGP、EGP And Incomplete

See

2022-07-15 Advanced network engineering （ nineteen ）BGP- State machine 、 The principle of interaction between peers 、 Factors that affect the establishment of peer relationships 、 Peer surface 、 Routing table 、 Detailed routing table 、 Routing properties _ Goose blog -CSDN Blog

06 optimization MED The attribute value is the smallest The routing

MED（Multi-Exit Discriminator, Multiple exit discriminator ） Is an optional non transitional attribute , It's a measure , Used to point out to external peers that they have entered this AS Preferred path for , That is, when entering this AS There are multiple times at the entrance of ,AS have access to MED Dynamically affect others AS Choose the path to enter .

MED The smaller the attribute value is BGP The better the route is .

MED Mainly used in AS Influence between BGP The right way .MED Be passed on to EBGP After peer , Peer in its AS Internal delivery routing , Take with you MED value , But pass the route to it again EBGP Peer time , By default, it will not carry MED attribute .

characteristic ：

MED At most, only two adjacent AS, received MED Attribute AS Will not pass it on to others AS.

MED Properties are similar to COST, It is applicable when a destination has multiple routes , And a AS When there are multiple entrances , Manually configurable MED Optimize the route .

Use the routing policy to modify （ stay AS Inner boundary routing modifier , influence AS Other routers in -export, Influence oneself -import）

[R5]acl 2000
[R5-acl-basic-2000]rule 5 permit source 11.11.11.11 0 

[R5]route-policy 1 permit node 10
[R5-route-policy]if-match acl 2000
[R5-route-policy]apply cost 20

[R5]bgp 200
[R5-bgp]peer 1.1.1.1 route-policy 1 import
[R5-bgp]compare-different-as-med
[R5-bgp]bestroute med-none-as-maximum

PS：

compare-different-as-med command . By default , Routers only compare from the same neighbor AS Of BGP The routing MED value , You can use this command to start from different AS The same route is also compared MED value .

bestroute med-none-as-maximum command . To configure BGP When selecting the best route , If there is no MED Value is treated as the maximum .

View the modification results

[R5]display bgp routing-table 

 BGP Local router ID is 5.5.5.5 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete


 Total Number of Routes: 11
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>   11.11.11.11/32     1.1.1.1         100                   0      100i
 * i                     6.6.6.6                    100        0      100i
 *>i  22.22.22.22/32     6.6.6.6         0          100        0      100i
 *                       1.1.1.1                               0      100i
 *>   33.33.33.33/32     1.1.1.1                               0      100i
 * i                     6.6.6.6                    100        0      100i
 *>   44.44.44.44/32     1.1.1.1                               0      100i
 * i                     6.6.6.6                    100        0      100i
 *>   55.55.55.55/32     0.0.0.0         0                     0      i
 *>i  66.66.66.66/32     6.6.6.6         0          100        0      i
 *>i  77.77.77.77/32     7.7.7.7         0          100        0      i

analysis ： Go to 11.11.11.11 Because of the next hop 1.1.1.1 The routing MED Change the value to 100, But because of the configuration bestroute med-none-as-maximum command , So go 11.11.11.11 and 22.22.22.22 Routing of ,MED The route in case of loss is the maximum , Are not preferred .

07 Preferably from EBGP Peer to peer routing （EBGP Routing priority is higher than IBGP route ）

If you arrive at a destination with 2 Different routes , One from IBGP Learning to , One from EBGP Learning to , Will be preferred EBGP Learned this .

08 optimization To Next_Hop Of IGP The smallest measure The routing

Refers to the bottom IGP The cost value of the protocol , for example OSPF、IS-IS

See

2022-04-09 Advanced network engineering （ 3、 ... and ）OSPF- measurements 、 Three major table items 、 neighbor _ Goose blog -CSDN Blog

2022-06-27 Advanced network engineering （ Twelve ）IS-IS- Cost type 、 Cost calculation 、LSP Processing mechanism 、 Route revocation 、 Route penetration _ Goose blog -CSDN Blog _ Routing computation overhead

09 optimization Cluster_List The shortest The routing

Relevant command

Configure the reflector

[R7-bgp]peer 6.6.6.6 reflect-client 

10 optimization Router ID（Orginator_ID） Smallest equipment Advertised routing

11 optimization Minimum IP Peer notification of address The routing

Refers to the size of the updated source address