Aug 22 2009
Inter-AS Option B – Revisited
Consider the topology below.
Watch the video below or download and watch it on your iphone.
iPhone
Aug 3 2009
Frame-Relay to VLAN Interworking – AToM
Consider the topology below.
Watch the video below or download and watch it on your ipod or iphone.
The commands used in the above video can be found below.
PE1
!
hostname PE1
!
frame-relay switching
!
mpls ldp router-id Loopback0 force
mpls label protocol ldp
!
pseudowire-class ZARAR
encapsulation mpls
interworking ip
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.1 255.255.255.252
mpls ip
!
interface Serial2/0
no ip address
encapsulation frame-relay
clockrate 128000
frame-relay interface-dlci 110 switched
frame-relay intf-type dce
!
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
connect ISMAIL Serial2/0 110 l2transport
xconnect 3.3.3.3 101 pw-class ZARAR
!
PE2
!
hostname PE2
!
frame-relay switching
!
mpls ldp router-id Loopback0 force
mpls label range 500 600
mpls label protocol ldp
!
pseudowire-class ZARAR
encapsulation mpls
interworking ip
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.6 255.255.255.252
mpls ip
!
interface FastEthernet1/1
xconnect 1.1.1.1 101 pw-class ZARAR
!
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
CE1
!
hostname CE1
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface Serial0
ip address 11.0.0.1 255.255.255.252
encapsulation frame-relay
ip ospf network point-to-point
frame-relay map ip 11.0.0.2 110 broadcast
!
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
CE2
!
hostname CE2
!
interface Loopback0
ip address 5.5.5.5 255.255.255.255
!
!
hostname CE2
!
interface Loopback0
ip address 5.5.5.5 255.255.255.255
!
interface FastEthernet0
ip address 11.0.0.2 255.255.255.252
ip ospf network point-to-point
!
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
Feb 28 2009
6PE – IPv6 over MPLS
6PE is a really cool feature which allows IPv6 islands to communicate with each other over an MPLS/IPv4 core network. IPv4 addresses space is fast running out so familiarising yourself with IPv6 is probably a good idea.
Consider the toplogy below.
Service providers can leverage their MPLS networks to deliver IPv6 solutions without having to rearchitect their networks. The PE devices are configured with IPv6 routing capability, however the P nodes have no IPv6 routing functionality enabled.
Data packets are encapsualted into MPLS frames on the ingress PE with two labels, the bottom of the stack label being the label assigned to the IPv6 prefix and the top label which is used to forward the packet has a label binding of the PE3s loopback 0 address.
From 6PE2 if we do a cef lookup for the IPv6 prefix connected to 6PE1 we see the following.
6PE2#sh ipv6 cef 2001:2::
2001:2::/64
nexthop 10.0.0.5 FastEthernet1/0 label 16 19
The bottom of stack label ie 19 is the ipv6 label and can be verified on 6PE2 as below.
6PE2#sh ip bgp ipv6 unicast labels
Network Next Hop In label/Out label
2001:2::/64 ::FFFF:1.1.1.1 nolabel/19
The top label ie 16 is generated from a recursive lookup which points to the remote 6PE device ie 6PE1s loopback address.
6PE2#sh ip cef 1.1.1.1
1.1.1.1/32
nexthop 10.0.0.5 FastEthernet1/0 label 16
6PE2#
the 6CEs can use an IPv6 IGP for 6PE-to-6CE connectivity or they can rely on static routing. In this case static routing has been configured as below.
ipv6 route ::/0 FastEthernet1/0 2001:2::2
Watch the video below or download it and watch it on your iPod or iPhone.
Feb 11 2009
BGP – Remove Private AS
The video below shows how to remove a private AS from BGP as-path list.
Consider the topology below.
AS65300 peers eBGP with R1. R1 then peers eBGP with R2.
R1 is then configured to remove all private ASs in the as-path when it advertises BGP routes to R2.
Watch the video below or download and watch it on your iPod or iPhone.
The commands used in thiss video are as below:
CE1
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0
ip address 10.0.0.1 255.255.255.252
!
router bgp 65300
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 10.0.0.2 remote-as 1
!
R1
!
interface FastEthernet1/0
ip address 10.0.0.2 255.255.255.252
!
interface FastEthernet1/1
ip address 10.0.0.5 255.255.255.252
!
router bgp 1
no synchronization
bgp log-neighbor-changes
neighbor 10.0.0.1 remote-as 65300
neighbor 10.0.0.6 remote-as 2
neighbor 10.0.0.6 remove-private-as
no auto-summary
!
R2
!
interface FastEthernet0
ip address 10.0.0.6 255.255.255.252
!
router bgp 2
bgp log-neighbor-changes
neighbor 10.0.0.5 remote-as 1
!
On R2 we can now see the bgp route 1.1.1.1/32 with the AS65300 in its as-path.
R2
!
R2#sh ip bgp
BGP table version is 2, local router ID is 10.0.0.6
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.0.0.5 0 1 i
R2#
Feb 7 2009
OSPF down bit and domain tag
Both the OSPF down bit and domain tag are modifications in OSPF which are used as loop prevention mechanisms. Why are there two mechanisms you ask. This is because type 5 LSAs do not contain the options field in the header. The options field is where the down bit is set. In LSA type 5 an external route tag is used to identify routes which have been redistributed from BGP into OSPF.
The external route tag value is a 32-bit value. The four highest bits are set to 1101 according to RFC 1745. The lowest 16 bits map to the BGP autonomous system (AS) number of the MPLS VPN backbone. you can set the VPN tag value manually within ospf using the command domain-tag <tag>.
To demonstrate both the down-bit and external route-tag consider the topology below. We will as part of the excersise change the external tag and see if we can induce a routing loop.
You can watch the video below, or alternativly you can download it and watch it on you iPod or iPhone.
I made this one in a bit of a hurry, so would appreciate some feedback.
Feb 1 2009
Controlling MPLS Label Distribution – Video
I was looking through my archives to remember how to configure “controlling label distribution” and realised that I had not not made a video for this subject, so here goes.
Consider the topology below.
As we all know, LDP assigns a Label for each IGP prefix and connected route in the RIB. Therefore when we use the “Control label distribution” feature we need to ensure the ACL we use, contains an access control entry(ACE) for the neighboring loopbacks. Each Label Switch Router(LSR) then advertises a label binding for each loopback.
Lets take R3s loopback for example. R3 advertises a label for its loopback to R2. R2 has an ACE for R3s loopback and therefore sends a label to R1. R1 now has an end to end LSP to R3. If on R2 you did not have an ACE for R3s loopback, you are effectivly breaking the LSP.
Watch how to configure it below, or download it and watch in on your iPod or iPhone.
The commands used in the above video can be seen below.
R1
!
no mpls ldp advertise-labels
mpls ldp advertise-labels for LOOPBACK0
mpls label protocol ldp
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet1/1
ip address 10.0.0.1 255.255.255.252
ip ospf network point-to-point
mpls ip
!
router ospf 1
router-id 1.1.1.1
network 1.1.1.1 0.0.0.0 area 0
network 10.0.0.0 0.0.0.3 area 0
!
ip access-list standard LOOPBACK0
permit 1.1.1.1
permit 2.2.2.2
permit 3.3.3.3
!
mpls ldp router-id Loopback0
!
R2
!
no mpls ldp advertise-labels
mpls ldp advertise-labels for LOOPBACK0
mpls label protocol ldp
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.2 255.255.255.252
ip ospf network point-to-point
mpls ip
!
interface FastEthernet1/1
ip address 10.0.0.5 255.255.255.252
ip ospf network point-to-point
mpls ip
!
ip access-list standard LOOPBACK0
permit 2.2.2.2
permit 3.3.3.3
permit 1.1.1.1
!
mpls ldp router-id Loopback0
!
R3
!
no mpls ldp advertise-labels
mpls ldp advertise-labels for LOOPBACK0
mpls label protocol ldp
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.6 255.255.255.252
ip ospf network point-to-point
mpls ip
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
network 3.3.3.3 0.0.0.0 area 0
network 10.0.0.4 0.0.0.3 area 0
!
ip access-list standard LOOPBACK0
permit 3.3.3.3
permit 1.1.1.1
permit 2.2.2.2
!
mpls ldp router-id Loopback0
Jan 23 2009
eBGP multihop
eBGP multihop can be used to loadshare traffic across multiple links between eBGP peers.
Consider the topology below.
By default eBGP sessions can only be established between directly connected interfaces. If you want to connect to a non-connected interface or to a non-connected neighbor, you have to use the eBGP-multihop feature.
For this to work, you need to add a static route or routes if you want to load share so that BGP knows how to reach the non-connected interface.
To prevent the creation of loops through oscillating routes, the multihop will not be established if the only route to the multihop peer is the default route (0.0.0.0).(CCO)
The Video below shows how eBGP-multihop can be used to load-share traffic across multiple links between eBGP peers. Only a single eBGP-multihop session is required, the underlying static routes will load share the traffic. This can be confirmed in the FIB.
(Download and watch the video below on your iPod or iPhone).
The commands used in the above scenario can be found below.
R1
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.1 255.255.255.252
!
interface FastEthernet1/1
ip address 10.0.0.5 255.255.255.252
!
router bgp 1
neighbor 2.2.2.2 remote-as 2
neighbor 2.2.2.2 ebgp-multihop 2
neighbor 2.2.2.2 update-source Loopback0
!
ip route 2.2.2.2 255.255.255.255 10.0.0.2
ip route 2.2.2.2 255.255.255.255 10.0.0.6
R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.2 255.255.255.252
!
interface FastEthernet1/1
ip address 10.0.0.6 255.255.255.252
!
interface Loopback1
ip address 192.168.1.1 255.255.255.0
!
router bgp 2
network 192.168.1.0
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 ebgp-multihop 2
neighbor 1.1.1.1 update-source Loopback0
!
ip route 1.1.1.1 255.255.255.255 10.0.0.1
ip route 1.1.1.1 255.255.255.255 10.0.0.5