IS-IS动态路由协议需要注意到几个问题

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Cisco527 2012-09-20 14:02:50

文章标签 的 router 动态 interface 是 文章分类 网络安全

IS-IS 需要注意到几个问题

一、IS-IS router type 和 interface Circuit Type、 adjacency type

router level-type 决定了路由器利用 lsp 建立、维护什么样的lsdb，如果是L1维护本 area 的LSDB, 如果是L2，则维护全局L2 LSDB，如果是 L1-l2 则维护所有的LSDB，同时向L1的router通过默认路由。

Circuit Type：默认 L1-L2， L1，L2

adjacency type：决定了接口通告 L1，或者L2 ，或者全部区域的LSP，有 L1 或者 L2，L1L2 。

Adjacency Building

Neighbors on point-to-point networks always become adjacent unless they do not see themselves in their neighbors' hello PDU and match on certain parameters. On broadcast networks and nonbroadcast multiaccess (NBMA) networks, the DIS (Designated Intermediate System) will become adjacent with its neighbors.

Two routers will become neighbors if the following parameters are agreed upon:

Level 1—The two routers sharing a common network segment must have their interfaces configured to be in the same area if they are to have a Level 1 adjacency.

Level 2—The two routers sharing a common network segment must be configured as Level 2 if they are in different areas and want to become neighbors.

Authentication—IS-IS allows for configuration of a password for a specified link, for an area, or for an entire domain.

A1/L1 -- A1/L1 -> L1

A1/L1 -- A1/L1L2 -> L1

A1/L1 -- A2/L1L2 ->

A1/L2 -- A1/L2 ->L2

A1/L2 -- A2/L1L2 -> L2

A1/L2 -- A2/L2 ->L2

A1/L1L2 -- A1/L1L2 -> L1L2

Comment: 不同area的 L1 接口不能形成邻接关系， L2 接口形成邻接关系与区域无关。一边说来只有修改 L1L2 接口的 circuit type 才有实际意义。

查看 router type

R2#sh clns protocol

IS-IS Router: <Null Tag>

System Id: IS-Type: level-1-2

Manual area address(es):

86.4809.0021

Routing for area address(es):

86.4809.0021

Interfaces supported by IS-IS:

Serial1/1 - IP

Serial1/0 - IP

Loopback0 - IP

Redistribute:

static (on by default)

Distance for L2 CLNS routes: 110

RRR level: none

Generate narrow metrics: level-1-2

Accept narrow metrics: level-1-2

Generate wide metrics: none

Accept wide metrics: none

R2#

查看接口 circuit type

R2#sh clns interface

FastEthernet0/0 is administratively down, line protocol is down

CLNS protocol processing disabled

Serial1/0 is up, line protocol is up

Checksums enabled, MTU 1500, Encapsulation HDLC

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 19 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x1, local circuit ID 0x100

Neighbor System-ID: 0010.0100.1001

Level-1 Metric: 10, Priority: 64, Circuit ID: 0020.0200.2002.00

Level-1 IPv6 Metric: 10

查看邻居 type

R2# sh clns neighbors

System Id Interface SNPA State Holdtime Type Protocol

0010.0100.1001 Se1/0 *HDLC* Up 26 L2 IS-IS

0030.0300.3003 Se1/1 *HDLC* Up 25 L1 IS-IS

R2#

二、IS-IS的 metric

Cisco IOS支持的metric style

R4(config-router)#metric-style ?

narrow Use old style of TLVs with narrow metric

transition Send and accept both styles of TLVs during transition

wide Use new style of TLVs to carry wider metric

R4(config-router)#metric-style

Narrow style:接口的 metric 默认为 10 （1-63），route/path 的 metric 10bit，最大为 1023 .

wide style: interface 24bit， route/path metric 32bit

Comment: 一般建议使用 wide metric 方便网络扩展。

三、DIS(Designated IS)

DIS 是指一个接口，在MA网络中， DIS接口和其他接口形成邻接关系，非DIS接口不形成邻接关系。

R4#sh clns interface

FastEthernet0/0 is up, line protocol is up

Checksums enabled, MTU 1497, Encapsulation SAP

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 8 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x1, local circuit ID 0x2

Level-2 Metric: 10, Priority: 64, Circuit ID: 0040.0400.4004.02

DR ID: 0040.0400.4004.02

Level-2 IPv6 Metric: 10

Number of active level-2 adjacencies: 1

Next IS-IS LAN Level-2 Hello in 1 seconds

Loopback0 is up, line protocol is up

Checksums enabled, MTU 1514, Encapsulation LOOPBACK

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching disabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 54 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x0, local circuit ID 0x1

Level-2 Metric: 10, Priority: 64, Circuit ID: 0040.0400.4004.01

DR ID: 0000.0000.0000.00

Level-2 IPv6 Metric: 10

Number of active level-2 adjacencies: 0

Next IS-IS LAN Level-2 Hello in 5 seconds

R4#

DIS 选举原则

1、接口优先级别

2、SNPA（MAC地址）的高低

R4(config-if)#isis priority 10

R4(config-if)#do show clns int f0/0

FastEthernet0/0 is up, line protocol is up

Checksums enabled, MTU 1497, Encapsulation SAP

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 50 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x1, local circuit ID 0x2

Level-2 Metric: 10, Priority: 10, Circuit ID: 0010.0100.1001.02

DR ID: 0010.0100.1001.02

Level-2 IPv6 Metric: 10

Number of active level-2 adjacencies: 1

Next IS-IS LAN Level-2 Hello in 4 seconds

R4(config-if)#

DIS 没有 backup DIS , 相应的解决备份问题的机制是DIS抢夺，代价是每抢夺一次会引起一组LSP的泛洪。同时IS-IS LSDB在LAN上不断同步，即CSNP的周期性发送，其实设计成周期性发送还有一个原因，那就是CSNP不要求有确认应答。

四、backbone area

IS-IS是通过连续的L2路由器来组成骨干CSNA网络分析社区4 @- U5 w4 }" T区，IS- IS的骨干区域是由连续的L2，L1/L2路由器构成的。L1 area 只要与一个L1/L2 连接就可以了。如果 L2 ， L1/L2 router不连续的话，也会出现网络分裂的问题。只能依靠网络设计避免，避免单链路，单路由器故障造成骨干区域分裂。 IS-IS在设计时应先定义好区域，骨干区域全为Level-2 Router，边界为Level-1-2 Router（最好规划到Level-1区域），末节区域为Level-1 Router。