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最新推荐文章于 2025-01-09 17:40:30 发布

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BGP Autonomous Systems

AS号：公有 0-64511

：私有:64512-65535

AS号查询

http://www.cidr-report.org/as6447/autnums.html

BGP Path-Vector Routing

AS相当于一个大路由器

AS-by-AS

BGP Characteristics

BGP is most appropriate when at least one of the following

conditions exists:

--- An AS allows packets to transit through it to reach other autonomous systems(for example ,it si a service provider).

--- An AS has multiple connections to other autonomous systems.

--Routing policy and route selection for traffic entering and leaving the AS must be manipulated.

BGP is not always appropriate,You do not have to use BGP if you have one of the following conditions:

---Limited understanding of route filtering and BGP path-selection process.

---A single connection to the Internet or another AS

---Lack of memory or processor power to handle constant updates on BGP routers.

电信---网通

1、管理

2、OSPF 10000条，ISIS,20000条，internet 10几万条

3、BGP策略路由

4、 ---扩展应用，ipv4、ipv6、vpnv4、MPLS

BGP Characteristic(Count.)

BGP is a path-vector protocol with the follow

enhancements over distance vector protocols:

---Reliable updates:runs on top of TCP (port 179)

---Incremental,triggered updates only

---Periodic keep-alive messages to verify TCP connectivity

---Rich metrics (called path vectors or attributes)

---Designed to scale to huge inter-networks(for example,the Internet)

BGP Databases(三张表)

Neighbor table

--List of BGP neighbors

BGP table（forwarding database）

---List of all networks learned from each neighbor

---Can contain multiple paths to destination networks

---Contains BGP attributes for each path

IP routing table

---List of best paths to destination networks

不做负载均衡

IBGP 200

EBGP 20

BGP Message Types

BGP defines the following message types:

Open

---Includes hold time and BGP router ID

Keepalive

Update

---Information for one path only(could be to multiple networks)

---Includes path attributes and networks

Notification

---When error is detected

---BGP connection closed after message is sent

_______________________________________________________________________

Explaining EBGP and IBGP

Peers = Neighbors

A "BGP peer," also known as a "BGP neighbor," is a specific term that is used for BGP speakers that have established a neighbor relationship
Any two routers that have formed a TCP connection to exchange BGP routing Information are called BGP peers or BGP neighbors.

External BGP

When BGP is running between neighbors that belong to different autonomous systems,it is called EBGP.
EBGP neighbors,by default,need to be directly connected.

Internal BGP

When BGP is running between neighbors within the save AS,it is called IBGP
The neighbors do not have to be directly connected.

IBGP in a Transit AS (ISP)

Redistributing BGP into an IGP (OSPF in this example) is not recommended.
Instead,run IBGP on all routers.

解决路由黑洞

1、物理线路FULL MESH

2、BGP邻居的FULL MESH

3、将BGP重分布到IGP(LAB)

4、MPLS（最好的解决方案）

IBGP In a NonTransit AS

EBGP水平分割

不接收含有本AS号的BGP路由。

IBGP

By default,routers learned via IBGP are never propagated to

other IBGP peers,so they need full-mesh IBGP

有条件的打破 IGBP水平分割。

IBGP

network hello邻居

通告路由

EBGP

Neighbor

network

R4上的配置

router bgp 4

bgp router-id 4.4.4.4

bgp log-neighbor-changes

neighbor 24.1.1.2 remote-as 1

R2上的配置

router bgp 1

bgp router-id 2.2.2.2

bgp log-neighbor-changes

neighbor 24.1.1.4 remote-as 4

R4#show ip bgp summary

BGP router identifier 4.4.4.4, local AS number 4

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

24.1.1.2 4 1 14 14 1 0 0 00:09:22 0

R2#show ip bgp neighbors

BGP neighbor is 24.1.1.4, remote AS 4, external link

BGP version 4, remote router ID 4.4.4.4

BGP state = Established, up for 00:02:00

Last read 00:00:03, last write 00:00:00, hold time is 180, keepalive interval is 60 seconds

Neighbor sessions:

1 active, is not multisession capable (disabled)

Neighbor capabilities:

Route refresh: advertised and received(new)

Four-octets ASN Capability: advertised and received

Address family IPv4 Unicast: advertised and received

Enhanced Refresh Capability: advertised and received

Multisession Capability:

Stateful switchover support enabled: NO for session 1

Message statistics:

InQ depth is 0

OutQ depth is 0

Sent Rcvd

Opens: 1 1

Notifications: 0 0

Updates: 1 1

Keepalives: 3 3

Route Refresh: 0 0

Total: 5 5

Default minimum time between advertisement runs is 30 seconds

For address family: IPv4 Unicast

Session: 24.1.1.4

BGP table version 1, neighbor version 1/0

Output queue size : 0

Index 1, Advertise bit 0

1 update-group member

Slow-peer detection is disabled

Slow-peer split-update-group dynamic is disabled

Sent Rcvd

Prefix activity: ---- ----

Prefixes Current: 0 0

Prefixes Total: 0 0

Implicit Withdraw: 0 0

Explicit Withdraw: 0 0

Used as bestpath: n/a 0

Used as multipath: n/a 0

Outbound Inbound

Local Policy Denied Prefixes: -------- -------

Total: 0 0

Number of NLRIs in the update sent: max 0, min 0

Last detected as dynamic slow peer: never

Dynamic slow peer recovered: never

Refresh Epoch: 1

Last Sent Refresh Start-of-rib: never

Last Sent Refresh End-of-rib: never

Last Received Refresh Start-of-rib: never

Last Received Refresh End-of-rib: never

Sent Rcvd

Refresh activity: ---- ----

Refresh Start-of-RIB 0 0

Refresh End-of-RIB 0 0

Address tracking is enabled, the RIB does have a route to 24.1.1.4

Connections established 1; dropped 0

Last reset never

Transport(tcp) path-mtu-discovery is enabled

Graceful-Restart is disabled

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 1

Local host: 24.1.1.2, Local port: 179

Foreign host: 24.1.1.4, Foreign port: 48615

Connection tableid (VRF): 0

Maximum output segment queue size: 50

Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)

Event Timers (current time is 0x31CD9):

Timer Starts Wakeups Next

Retrans 5 0 0x0

TimeWait 0 0 0x0

AckHold 4 2 0x0

SendWnd 0 0 0x0

KeepAlive 0 0 0x0

GiveUp 0 0 0x0

PmtuAger 0 0 0x0

DeadWait 0 0 0x0

Linger 0 0 0x0

ProcessQ 0 0 0x0

iss: 3917151808 snduna: 3917151946 sndnxt: 3917151946

irs: 1610121879 rcvnxt: 1610122017

sndwnd: 16247 scale: 0 maxrcvwnd: 16384

rcvwnd: 16247 scale: 0 delrcvwnd: 137

SRTT: 487 ms, RTTO: 3168 ms, RTV: 2681 ms, KRTT: 0 ms

minRTT: 7 ms, maxRTT: 1000 ms, ACK hold: 200 ms

Status Flags: passive open, gen tcbs

Option Flags: nagle, path mtu capable

IP Precedence value : 6

Datagrams (max data segment is 1460 bytes):

Rcvd: 11 (out of order: 0), with data: 5, total data bytes: 137

Sent: 10 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 5, total data bytes: 137

Packets received in fast path: 0, fast processed: 0, slow path: 0

fast lock acquisition failures: 0, slow path: 0

TCP Semaphore 0xF49FCF8C FREE

R2#show tcp brief

TCB Local Address Foreign Address (state)

F1559798 24.1.1.2.179 24.1.1.4.48615 ESTAB

F4BFA5F8 2.2.2.2.17210 3.3.3.3.179 ESTAB

IBGP建议用环回接口建邻居。

更新源

NEI 24.1.1.2 NEI 24.1.1.4

US:24.1.1.4 US 24.1.1.2

NEI 3.3.3.3 NEI 2.2.2.2

US 12.1.1.2 US13.1.1.3

R2上的配置

router ospf 110

router-id 2.2.2.2

network 2.2.2.0 0.0.0.255 area 0

network 12.1.1.0 0.0.0.255 area 0

router bgp 1

bgp router-id 2.2.2.2

bgp log-neighbor-changes

neighbor 3.3.3.3 remote-as 1

neighbor 3.3.3.3 update-source Loopback0

neighbor 24.1.1.4 remote-as 4

R1上的配置

router ospf 1

router-id 1.1.1.1

network 12.1.1.0 0.0.0.255 area 0

network 13.1.1.0 0.0.0.255 area 0

R3上的配置

router ospf 110

router-id 3.3.3.3

network 3.3.3.0 0.0.0.255 area 0

network 13.1.1.0 0.0.0.255 area 0

router bgp 1

bgp router-id 3.3.3.3

bgp log-neighbor-changes

neighbor 2.2.2.2 remote-as 1

neighbor 2.2.2.2 update-source Loopback0

Example ebgp-multihop command

A路由器配置

router bgp 65102

neighbor 1.1.1.1 remote-as 65101

neighbor 1.1.1.1 update-source Loopback 0

neighbor 1.1.1.1 ebgp-multihop 2

ip route 1.1.1.1 255.255.255.255 192.168.1.18

ip route 1.1.1.1 255.255.255.255 192.168.1.34

B路由器配置

router bgp 65101

neighbor 2.2.2.2 remote-as 65102

neighbor 2.2.2.2 update-source Loopback 0

neighbor 2.2.2.2 ebgp-multihop 2

ip route 2.2.2.2 255.255.255.255 192.168.1.17

ip route 2.2.2.2 255.255.255.255 192.168.1.33

R4#show ip bgp

BGP table version is 2, local router ID is 4.4.4.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*> 4.4.4.0/24 0.0.0.0 0 32768 i

*:为可用的，>:最优的路由

R2#show ip bgp

BGP table version is 2, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*> 4.4.4.0/24 24.1.1.4 0 0 4 i

R3#show ip bgp

BGP table version is 1, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

* i 4.4.4.0/24 24.1.1.4 0 100 0 4 i

没有>:（不优的路由）

1、不会进路由表。

2、不会给其他BGP邻居传。

BGP路由优的条件:

1、同步（从IGP学习到/no syn）

2、下一跳

R3(config)#router bgp 1

R3(config-router)#no sy

R3(config-router)#no synchronization

R2(config-router)#neighbor 3.3.3.3 next-hop-self

R3#show ip bgp

BGP table version is 2, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 4.4.4.0/24 2.2.2.2 0 100 0 4 i

BGP Synchronization

Synchronization rule:Do not use or advertise to an external neighbor a route learned by IBGP until a

matching route has been learned from an IGP

Ensures consistency of information throughout the AS
Safe to have it off only if all routers in the transit path in the AS are running full-mes IBGP:off by default in Cisco software release 12.2(8)

Router(config-router)#

no synchronization

Disables BGP synchronization so that a router will advertise routes in IGP without learning them in an IGP

Router (config-router)#

synchronization

Enables BGP synchronization so that a router will not advertise routers in BGP until it learns them in an IGP

Using a peer group

Router(config-router)#

neighbor peer-group-name peer-group

This command creates a peer group.

Router(config-router)#

neighbor ip-address peer-group peer-group-name

This command defines a template with parameters set for a group of neighbors instead of individually.
This command is useful when many neighbors have the same outbound policies.
Members can have a different inbound policy.
Updates are generated once per peer group.
Configuration is simplified.

R1#show run | b r b

router bgp 1

bgp router-id 1.1.1.1

bgp log-neighbor-changes

neighbor aaa peer-group

neighbor aaa remote-as 1

neighbor aaa update-source Loopback0

neighbor 2.2.2.2 peer-group aaa

neighbor 3.3.3.3 peer-group aaa

R4#show run | b r b

router bgp 4

bgp router-id 4.4.4.4