Problem about"ISIS as the PE/CE Protocol in BGP/MPLS VPNs"

I read a IETF document  about This,but I have some problems to ask for explaination:

"

4.2  Carry IS-IS imformation with BGP Extended communities

     Per [VPN], BGP is in charge of distributing VPN-IP routes accross
     the VPN backbone. It is very useful of carrying some of the
     important original IS-IS route information by BGP with BGP
     extended communities. These "important" original IS-IS route
     information are listed as follows:

     -- IS-IS Route Type Extended Communites Attribute.

        This attribute is required, which is enconded with a two-byte
        type field and the type is 0201.  The third byte is encoded
        as follows:

        -- Level type: The first bit. When it is set 0, it indicates
           level-1 type route and the value of 1 indicates level-2 type
           route.
.........................................---------------------------THis is from This document

 

BUT in my lab :CE1--PE1======PE2---CE2

PE1#show ip route vrf vpn14 isis | inc ^i_
i L1     1.1.1.1 [115/20] via 12.0.0.1, 03:05:38, Ethernet1/0
PE1#

PE2#show ip route vrf vpn14 bgp | inc ^B___
B        1.1.1.1 [200/20] via 2.2.2.2, 01:22:49
PE2#


R3#show ip bgp vpnv4 all 1.1.1.1/32
BGP routing table entry for 14:14:1.1.1.1/32, version 28
Paths: (1 available, best #1, table vpn14)
  Not advertised to any peer
  Local, (Received from a RR-client)
    2.2.2.2 (metric 20) from 2.2.2.2 (2.2.2.2)
      Origin incomplete, metric 20, localpref 100, valid, internal, best

----------------------------------------------------NOT INCLUDE ANY INFOMATION ABOUT THE "original ISIS prefix"
      Extended Community: RT:14:14
      mpls labels in/out nolabel/18
R3#

 

 

##################################################

##################################################

4.3  Route loop prevention on PEs

     As per the diagram of 4, when PE1 and PE2 both import bgp routes
     into their attached CE sites, the route
     loop will happen on both PEs.

     To avoid the route loop, it is assumed here that both PE1 and
     PE2 act as L1/2 router and there exists level-1 adjacency between
     each PE-CE link. The mechanism of how to avoid route loop with
     up/down bit in IS-IS level-1 LSP is specified in [ROUTE-LEAKING].

------------------thIS IS ALSO FROM THIS IETF DOCUMENT

 

 

but in may lab :

PE2#show isis nei

Tag global:
System Id      Type Interface   IP Address      State Holdtime Circuit Id
PE1             L2   Et1/1       23.0.0.2        UP    23       PE1.03             

Tag vpn14:
System Id      Type Interface   IP Address      State Holdtime Circuit Id
CE2             L1   Et1/2       34.0.0.4        UP    23       CE2.01             

R4#show ip route isis | inc ^i_
i L1     1.1.1.1 [115/10] via 34.0.0.3, 01:28:47, Ethernet1/2-------------------NOT "ia" BUT "i L1"
R4#

 

my IOS version ::

Cisco IOS Software, 7200 Software (C7200-ADVENTERPRISEK9-M), Version 12.2(33)SRE1, RELEASE SOFTWARE (fc2)

Comments

  • if you have one CPE dual homed to two PE routers, then you may have use 'distance 201 ip' under ISIS process to avoide loops. i have tested this in GNS. it works fine for my network setup.

     

    down bit option is usful if you have two CPE dual homed to two PE and there is a backdoor link between CPEs. 

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