Friday, December 17, 2010

concise MPLS notes CCNP/CCIP/CCIE



M PLS :

What is MPLS (Multi-protocol label switching ) : MPLS is a packet-forwarding technology which uses labels to make data forwarding decisions. With MPLS, the Layer 3 header analysis is done just once when the packet enters the MPLS domain. MPLS impose a label in a packet between data link layer  and network layer . label 0-15 are reserved label.

LSR : label switching router /provider router which called as P router

edge LSR / provider edge (PE) router :  which is called as PE router

Label distribution protocol (LDP)

TDP : tag distribution protocol by Cisco    uses TCP /UDP port 711 uses 224.0.0.2 all router in multicast subnet

LDP : uses TCP/UDP port 646 and 224.0.0.2


Forwarding information  base (FIb) which CEF  table    :  “show ip cef” will show you details

label information Base (LiB) “show MPLS  ldp binding” command will show details of LIB.

label forwarding information base (LFIB )  which is action table,  “ show MPLS forwarding-table” command will show forward table .

MPLS default hello interval is 5 sec and hold time is 15 second

MPLS control plane :

where L3 routing protocol exist

where label exchange protocol exist LDP/TDP

control plane take care of exchanging routing information conjunct with LDP.
LDP assigns a label to a route for its incoming and outgoing interface, for
instance network 10.0.0.0/8 gets a label 24 for incoming interface and 25 for outgoing
interface

only PE router looks routing lookup and does label removal .


MPLS Data plane /forwarding plane:

sends data based on L3 or L2 information

takes care of label swapping in other word  data plane take cares of LFIB


MPLS process :

1.router build routing table by routing protocol

2. the mpls-enabled routers assign label to each route

3. the routers advertise the route to other LSRs

4. all LSRs build their FIBs, LIBs and LFIBs table


Some Important command :

shw mpls ldp discovery details

show mpls ldp parameters

show mpls forwarding table

show mpls ldp binding

show mpls ip binding


PHP = penultimate hop popping  does not work in ATM ( a label gets remove by the P router before it sending to PE router , to reducing table lookup in PE router)

VRF = virtual routing and forwarding

MPLS VPN terms :

Route Distinguisher : (RD) keep customer routes unique with a number

Route Target (RT) : route target number can be use for import and export routes , has to be identical on PE router

.
PE /Edge LSR router keeps following information :

control plane :  routing protocol
                         ip routing table
                         label distribution protocol

Data plane     :  ip forwarding table
                         label forwarding table

in ATM VPI and VCI is used  as label , and its called cell mode MPLS

MPLS traffic engineering require OSPF or is-is routing protocol

LSP = label switch path  , LSP build by routing protocol

in MPLs VPN  route summarization should not be use , because in vpn end to end LSPs are required

the LSR assigns a label to a network connected locally and advertise the to all neighbor , saying  this is the label for my network .

MPLS is defend on IGP protocol for loop prevention although it has 8 bit TTL value , when time to leave value decrease to 0 the packet gets drop , to prevent endless loop. TTL value by default on in Cisco router.

but can be disable , the benefit is if some one does trace route it will show core LSR in trace if TTL blocked in LSR. if TTL disable , should have to disable in all Router .


MPLS  frame mode uses per platform labels , this is not secure , and causes label spoofing attack , can call it unsolicited downstream label distribution

MPLS ATM mode uses per interface labels , ATM  use downstream on demand approach

router with higher ip address initiate TCP session , loopback beats physical interface , higher is batter

uni-cast IP address also can be used to form neighbor , instead 224.0.0.2 .

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