The MPLS-OPS Archive

[Venko Moyankov <venkom@mobikom.com>]

Hi all,

I've searched the list achieve for last 6 months, but didn't find any
discussion on this topic. Please excuse me if I missed it.

I need to make MPLS VPN with very large number of prefixes received from
CE (about 104k - the full internet BGP) and limited number of CEs. I'm
using 3660 and 7206 VXR as PEs with 256M RAM each. To be more precise
I'm using tag-switching, not MPLS. Two PE are directly connected
(without P) with FE.
Did anyone make something like this and is it working OK?

Now on 3660 PE I have only one vrf with about 104k prefixes, it has
about 80M free RAM.

==========================================================
3660#sho ip bgp vpnv4 vrf test1 summary 
BGP router identifier 212.5.128.239, local AS number 8795
BGP table version is 211855, main routing table version 211855
104142 network entries and 104141 paths using 18849642 bytes of memory
34991 BGP path attribute entries using 2102220 bytes of memory
15308 BGP AS-PATH entries using 437108 bytes of memory
12 BGP community entries using 288 bytes of memory
1 BGP extended community entries using 24 bytes of memory
103 BGP route-map cache entries using 1648 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP activity 104868/551 prefixes, 107052/1875 paths, scan interval 15
secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down 
State/PfxRcd
62.176.103.246  4  8262   37636      42   211855    0    0 00:37:36  
104138

3660#sho mem
                Head    Total(b)     Used(b)     Free(b)   Lowest(b) 
Largest(b)
Processor   62354920   191543008   108167660    83375348    83362164   
78173696
      I/O    DA00000    39845888     3530740    36315148    35734104   
33911996
==========================================================

Every minite the routers says:

%TAGCON-3-LCLTAG_ALLOC: Cannot allocate local tag

It has assigned a unique tag for _every_ prefix it has learned!

This behavior is completely different from the case with tag-switching
and bgp in global routing table. In global routing table it uses one tag
for every next hop and all prefixes are with the same tag:

Let select two random prefixes - 63.101.83.0/24 and 63.101.128.0/24

===========================================================
In global routing table:
7206#sho ip cef 63.101.83.0   
63.101.83.0/24, version 331960, cached adjacency to ATM3/0.1
0 packets, 0 bytes
  Flow: AS 0, mask 24
  tag information from 146.188.0.178/32, shared, unshareable
    local tag: 59
  via 146.188.0.178, 0 dependencies, recursive
    next hop 146.188.0.178, ATM3/0.1 via 146.188.0.178/32
    valid cached adjacency
    tag rewrite with AT3/0.1, point2point, tags imposed: {}

7206#sho ip cef 63.101.128.0
63.101.128.0/24, version 481995, cached adjacency to ATM3/0.1
0 packets, 0 bytes
  Flow: AS 0, mask 24
  tag information from 146.188.0.178/32, shared, unshareable
    local tag: 59
  via 146.188.0.178, 0 dependencies, recursive
    next hop 146.188.0.178, ATM3/0.1 via 146.188.0.178/32
    valid cached adjacency
    tag rewrite with AT3/0.1, point2point, tags imposed: {}
7206#sho tag-switching forwarding-table tag 59
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop    
tag    tag or VC   or Tunnel Id      switched   interface              
59     Untagged    146.188.0.178/32  63314075   AT3/0.1    point2point  
===========================================================
In vrf:
3660#sho ip cef vrf test1 63.101.83.0   
63.101.83.0/24, version 5003, cached adjacency 62.176.103.246
0 packets, 0 bytes
  tag information set
    local tag: 5876
  via 62.176.103.246, 0 dependencies, recursive
    next hop 62.176.103.246, FastEthernet0/0.104 via 62.176.103.246/32
    valid cached adjacency
    tag rewrite with Fa0/0.104, 62.176.103.246, tags imposed: {}
3660#sho ip cef vrf test1 63.101.128.0  
63.101.128.0/24, version 4840, cached adjacency 62.176.103.246
0 packets, 0 bytes
  tag information set
    local tag: 5689
  via 62.176.103.246, 0 dependencies, recursive
    next hop 62.176.103.246, FastEthernet0/0.104 via 62.176.103.246/32
    valid cached adjacency
    tag rewrite with Fa0/0.104, 62.176.103.246, tags imposed: {}
3660#sho tag-switching forwarding-table tags 5876
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop    
tag    tag or VC   or Tunnel Id      switched   interface              
5876   Untagged    63.101.83.0/24[V] 0          Fa0/0.104 
62.176.103.246 
3660#sho tag-switching forwarding-table tags 5689
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop    
tag    tag or VC   or Tunnel Id      switched   interface              
5689   Untagged    63.101.128.0/24[V] 0          Fa0/0.104 
62.176.103.246 
===========================================================

Tag-switching forwarding table in VPN environment is extremely large and
all tags are exactly the same - with the same next hop and outgoing
interface. Why this happens? Do we really need 100k equal tags?

Does anybody know if this is a bug in MPLS VPN implementation, or
missing a feature, ot this is the right way?
I also believe that the same number of prefixes consume much more RAM in
MPLS VPN environment than in global space. 

Thanks in advance
Venko Moyankov
RTC Ltd. / Mobikom

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