IS-IS All in One Lab(Basic&Route.Summarization&DIS&BGP.Interaction&FD/FRR.Fast.C

Latest reply: Jun 23, 2015 15:51:24 2606 2 1 0

IS-IS All in One Lab(Basic&Route Summarization&DIS&Interaction with BGP&FD/FRR Fast Convergence)

IS-IS All in One Lab(Basic&Route.Summarization&DIS&BGP.Interaction&FD/FRR.Fast.C-1256777-1

Section I Basic IS-IS Functions

IS-IS is my weakest routing protocol, so I need to learn it carefully.

The first step is to configure IP address for all interfaces.

IS-IS configuration

1.Is-level 2.Network-entity [10(ISIS area).0000.0000.0001(serial No.).00] 3. Interface enable isis

With this configuration, we can ping from each other in AS 65008.

Please don’t forget to enable isis for those loopback interfaces.

 

Section II Route Summarization

From ISIS routing table of RouterD, we can see:

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags

-------------------------------------------------------------------------------

192.168.2.0/24       20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

10.5.1.0/24          30         NULL    GE0/0/1         10.2.1.1        A/-/-/-

192.168.1.0/24       20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

192.168.3.0/24       20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

10.1.1.0/24          20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

10.2.1.0/24          10         NULL    GE0/0/1         Direct          D/-/L/-

10.3.1.0/24          20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

This is complicated, we want to make the routing table brief. So we can make RouterC to summarize the routes from RouterA: [RouterC-isis-1]summary 192.168.0.0 255.255.0.0 level-1-2.

After that, we can have a bridge routing table of RouterD.

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags

-------------------------------------------------------------------------------

10.5.1.0/24          30         NULL    GE0/0/1         10.2.1.1        A/-/-/-

192.168.0.0/16       20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

10.1.1.0/24          20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

10.2.1.0/24          10         NULL    GE0/0/1         Direct          D/-/L/-

10.3.1.0/24          20         NULL    GE0/0/1         10.2.1.1        A/-/-/-

Still we can ping 192.168.2.1 from RouterD, why? For RouterC keeps the detailed routing table as below:

                        ISIS(1) Level-1 Forwarding Table

                        --------------------------------

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags

-------------------------------------------------------------------------------

192.168.2.0/24       10         NULL    GE0/0/0         10.1.1.1        A/-/L/-

10.5.1.0/24          20         NULL    GE0/0/0         10.1.1.1        A/-/L/-

                                        GE0/0/2         10.3.1.2      

192.168.1.0/24       10         NULL    GE0/0/0         10.1.1.1        A/-/L/-

192.168.3.0/24       10         NULL    GE0/0/0         10.1.1.1        A/-/L/-

10.1.1.0/24          10         NULL    GE0/0/0         Direct          D/-/L/-

10.2.1.0/24          10         NULL    GE0/0/1         Direct          D/-/L/-

10.3.1.0/24          10         NULL    GE0/0/2         Direct          D/-/L/-

                        ISIS(1) Level-2 Forwarding Table

                        --------------------------------

 

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags

-------------------------------------------------------------------------------

10.1.1.0/24          10         NULL    GE0/0/0         Direct          D/-/L/-

10.2.1.0/24          10         NULL    GE0/0/1         Direct          D/-/L/-

10.3.1.0/24          10         NULL    GE0/0/2         Direct          D/-/L/-

ISIS is a funny routing protocol for it keeps two forwarding tables. It’s just like my father. My father used to have two pack of cigarettes, the better one for guests while the worse one for himself. In the same way, ISIS uses level-1 forwarding table for level1 area, level-2 table for level-2 area.

 

Section III DIS

DIS is just like DR of OSPF, class head to handle ISIS routing business. One broadcast domain has one DIS, but there is no backup DIS.

With [RouterC]display isis interface, we can see who is DIS or not. The one with biggest MAC is DIS, which is a little different from OSPF where biggest IP address is preferred.

 

                       Interface information for ISIS(1)

                       ---------------------------------

 Interface       Id      IPV4.State          IPV6.State            MTU  Type DIS  

 GE0/0/0         001         Up                 Down         1497 L1/L2 No/No

 GE0/0/1         002         Up                 Down         1497 L1/L2 No/No

 GE0/0/2         003         Up                 Down         1497 L1/L2 No/No

I have a question, is it possible to change GE0/0/0 DIS of level-1 area? Yeah, of course.

[RouterC-GigabitEthernet0/0/0]isis dis-priority 100(Default value is 64)

After change, we can see GE0/0/0 becomes L1 DIS immediately, no need to reset process like OSPF does.

             Interface information for ISIS(1)

                       ---------------------------------

 Interface       Id      IPV4.State          IPV6.State      MTU  Type  DIS  

 GE0/0/0         001         Up                 Down         1497 L1/L2 Yes/No

 GE0/0/1         002         Up                 Down         1497 L1/L2 No/No

 GE0/0/2         003         Up                 Down         1497 L1/L2 No/No

What’s the standard? The router with higher performance should be selected as DIS.

 

Section IV Interaction with BGP

We’ll talk about BGP later, but here we talk about basic steps to configure BGP.

1.       BGP AS number 2. Peer IP address AS number 3. IPv4 unicast, network Done.

When we finished, I can’t ping other routers from RouterE, why? For different routing protocols can’t interact with each other by default.

    We need to use

[RouterE-bgp]import-route isis 1

    I make a foolish mistake. I think RouterE imports ISIS routes of RouterB, which is totally wrong. In fact, RouterE imports ISIS routes to its BGP, then its BGP sends those routes to RouterE’s BGP.

 [RouterB-bgp]import-route isis 1

Now we can see RouterE’s routing table as below:

[RouterE]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: 9

      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 

 *>   10.1.1.0/24        10.4.1.1        20                    0      65008?

 *>   10.2.1.0/24        10.4.1.1        20                    0      65008?

 *>   10.3.1.0/24        10.4.1.1        0                     0      65008?

 *>   10.4.1.0/24        0.0.0.0         0                     0      i

                         10.4.1.1        0                     0      65008i

 *>   10.5.1.0/24        10.4.1.1        0                     0      65008?

 *>   192.168.1.0        10.4.1.1        10                    0      65008?

 *>   192.168.2.0        10.4.1.1        10                    0      65008?

 *>   192.168.3.0        10.4.1.1        10                    0      65008?

But I still can’t ping from RouterE to RouterA/C/D, I can only ping other interfaces from RouterE with success. Why? Because there is no external route of RouterE on RouterA/C/D. Luckily, I know there is a route leaking function to resolve this, or else I’ll try hard in vain here.

Is there any other way?

Actually I only need to add a default route on RouterC

IP route-static 0.0.0.0 0.0.0.0 10.3.1.2

The default route will be transferred to RouterA by L1 area, so we can ping RouterA from RouterE.

                        --------------------------------

 

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags

-------------------------------------------------------------------------------

0.0.0.0/0            10         NULL    GE0/0/0         10.1.1.2        A/-/-/-

The default route can’t be transfed to RouterD by L2 area, so we can’t ping RouterD by RouterE, so we still need route leaking to resolve that. Route leaking in invented without reason if my default way cant’ resolve the issue completely.

 

Section V BFD/FRR Fast Convergence

Now we can see routing table of RouterA, there’re two routes to 10.3.1.0.

10.3.1.0/24          20         NULL    GE0/0/1         10.5.1.2        A/-/-/-

                                        GE0/0/0         10.1.1.2 

When I configure GE0/0/1 cost as 21, then there is only one route remaining.

10.3.1.0/24          20         NULL    GE0/0/0         10.1.1.2        A/-/-/-

Now GE0/0/1 link becomes backup link.

I disable GE0/0/0, the ISIS isn’t bad and will switch to backup link quickly, but when I enable GE0/0/0, the ISIS needs several seconds to switch to main link again.

So I can use BFD to have a comparison.

[RouterC]bfd ctoa bind peer-ip 10.1.1.1 interface GigabitEthernet 0/0/0

Don’t forget about Commit command.

[RouterC]display bfd session all

--------------------------------------------------------------------------------

Local Remote     PeerIpAddr      State     Type        InterfaceName           

--------------------------------------------------------------------------------

1     2          10.1.1.1        Up        S_IP_IF     GigabitEthernet0/0/0    

--------------------------------------------------------------------------------

     Total UP/DOWN Session Number : 1/0

Now BFD session is up.

    When we disable GE0/0/0 of RouterA, we can see ISIS 256 ne

ighbor 0000.0000.0003 was Down on interface GE0/0/0 because the BFD node was down, there is no doubt that BFD is quick.

FRR has already been talked about in OSPF and it also has the same function as BFD, so I just let it go.

 

 

 

 

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user_2790689 Created Mar 11, 2015 09:04:12 Helpful(0) Helpful(0)

Thank you for sharing.
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johnston78 Created Jun 23, 2015 15:51:24 Helpful(0) Helpful(0)

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