From: Ahamed Sadayan-Abdul-Hutha (asadayan) (asadayan@cisco.com)
Date: Tue Mar 03 2009 - 23:54:43 ARST
Folks,
Why do we need the info on the mpls forwarding table to get label
switched ? Am I missing some thing here ?
My understanding is mpls forwarding table information is gathered only
using LDP.
If we use bgp to exchange labels, even though the information is not
populated under mpls forwarding table, you will get label switched based
on the labels exchanged
via bgp.
I have a example here to share,
R4#show ip ro vrf ce1
Routing Table: ce1
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS
level-2
ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, Loopback1
10.0.0.0/32 is subnetted, 1 subnets
B 10.1.1.1 [20/0] via 150.1.3.3, 00:12:51
10.1.1.1 is learned across vrf and it's next hop address is 150.1.3.3
R4#show ip bgp vpnv4 all labels
Network Next Hop In label/Out label
Route Distinguisher: 100:1 (ce1)
10.1.1.1/32 150.1.3.3 nolabel/18
20.1.1.0/24 0.0.0.0 19/aggregate(ce1)
R4 is receiving label 18 from the remote PE for the prefix 10.1.1.1/32
R4#show mpls forwarding-table [ It doesn't have the next hop on the mpls
forwarding table]
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
18 Pop tag 150.1.24.2/32 0 Fa0/1 150.1.24.2
19 Aggregate 20.1.1.0/24[V] 1560
R4#show ip route bgp
150.1.0.0/16 is variably subnetted, 7 subnets, 2 masks
B 150.1.3.3/32 [20/10] via 150.1.24.2, 00:16:42
B 150.1.2.2/32 [20/0] via 150.1.24.2, 00:16:42
B 150.1.13.0/24 [20/10] via 150.1.24.2, 00:16:42
B 150.1.12.0/24 [20/0] via 150.1.24.2, 00:16:42
R4#show ip bgp ipv4 unicast labels [ My local label exchange is using
bgp instead of ldp]
Network Next Hop In Label/Out Label
150.1.2.2/32 150.1.24.2 nolabel/imp-null
150.1.3.3/32 150.1.24.2 nolabel/16
150.1.4.4/32 0.0.0.0 imp-null/nolabel
150.1.12.0/24 150.1.24.2 nolabel/imp-null
150.1.13.0/24 150.1.24.2 nolabel/17
150.1.24.0/24 0.0.0.0 imp-null/nolabel
150.1.24.0/24 150.1.24.2 imp-null/imp-null
150.1.24.2/32 0.0.0.0 18/nolabel
150.1.24.4/32 150.1.24.2 nolabel/18
R4#show ip cef vrf ce1 10.1.1.1
10.1.1.1/32, version 28, epoch 0, cached adjacency 150.1.24.2
0 packets, 0 bytes
tag information set
local tag: VPN-route-head
fast tag rewrite with Fa0/1, 150.1.24.2, tags imposed: {16 18}
via 150.1.3.3, 0 dependencies, recursive
next hop 150.1.24.2, FastEthernet0/1 via 150.1.3.3/32
valid cached adjacency
tag rewrite with Fa0/1, 150.1.24.2, tags imposed: {16 18}
R4#
This shows multiple recursive lookup but the tags imposed are the next
hop tag 150.1.3.3/32 (remote pe) and the vpn tag 16
R4#ping vrf ce1 10.1.1.1 source 20.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 20.1.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/18/20 ms
R4#
There is an end to end connectivity across vpns.
Thanks
Ahamed
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Roman Rodichev
Sent: Tuesday, March 03, 2009 1:53 PM
To: 'Peter Svidler'; ccielab@groupstudy.com;
smorris@internetworkexpert.com
Subject: RE: MPLS send-label
Yes, if it's the last BGP session in a chain, then you'll need to
redistribute routes into something. The reason for it is that LFIB will
not populate until there's an "IN" label for the prefix created by the
router.
IOS won't create the IN label until it's either:
1. Redistributed into some IGP (it doesn't have to be a real IGP in use,
a simple "router ospf 1" + "redistribute bgp X subnets" will do) 2. The
prefix has to be forwarded on by BGP to another eBGP or iBGP send-label
peer.
If you do "show ip bgp labels" and you don't see an "In" label for the
prefix, the prefix will not appear in the LFIB.
Roman Rodichev
5xCCIE #7927 (R&S, Security, Voice, Storage, Service Provider)
Instructor, Content Developer ieMentor Corporation
http://www.iementor.com
Y!M: roman7927
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Peter Svidler
Sent: Tuesday, March 03, 2009 3:35 PM
To: ccielab@groupstudy.com; 'Roman Rodichev';
smorris@internetworkexpert.com
Subject: RE: MPLS send-label
ok again :)
so when i peer from the loopbacks , even though i receive the labels via
BGP ..it does not automatically gets installed in the LFIB ..which means
another way is required ( such as redistributing BGP into IGP ) to get
it done .
and for the RFC thing ..probably the Cisco lab guys have to ask
questions based on that :)))
--- On Tue, 3/3/09, Scott Morris <smorris@internetworkexpert.com> wrote:
From: Scott Morris <smorris@internetworkexpert.com>
Subject: RE: MPLS send-label
To: "'Peter Svidler'" <doubleccie@yahoo.com>, ccielab@groupstudy.com,
"'Roman Rodichev'" <roman@iementor.com>
Date: Tuesday, March 3, 2009, 4:13 PM
Then you'll need to have a recusive lookup to get to that loopback
address!
And a label to match!
Scott
PS. Your eBGP peers are SUPPOSED to (by RFC) be peering with directly
connected interfaces. :)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Peter Svidler
Sent: Tuesday, March 03, 2009 3:57 PM
To: ccielab@groupstudy.com; Roman Rodichev
Subject: RE: MPLS send-label
Hi Roman ,
what if the peering is not from the directly connected IP addressing but
from the loopbacks ?
--- On Tue, 3/3/09, Roman Rodichev <roman@iementor.com> wrote:
From: Roman Rodichev <roman@iementor.com>
Subject: RE: MPLS send-label
To: "'Peter Svidler'" <doubleccie@yahoo.com>, ccielab@groupstudy.com
Date: Tuesday, March 3, 2009, 3:54 PM
No you don't have to. The router that receives BGP routes with labels
will put them into the LFIB.
Roman Rodichev
5xCCIE #7927 (R&S, Security, Voice, Storage, Service Provider)
Instructor, Content Developer ieMentor Corporation
http://www.iementor.com
Y!M: roman7927
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Peter Svidler
Sent: Tuesday, March 03, 2009 2:50 PM
To: ccielab@groupstudy.com
Subject: MPLS send-label
Folks ,
just i want to confirm this , when i use the IPV4 send-label option
between two PE's running IPV4
even though the labels are send via BGP , it does not insall
automatically in the MPLS table , i still need to redistribute BGP into
IGP to get this the prefixes installed in the MPLS forwarding table ..is
this correct ?
Blogs and organic groups at http://www.ccie.net
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