14th Lecture - Networking

[k2s]

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[k2s]

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[k2s]

In addition to above, we have some additional ( mostly not used but are imp) are :


11. DPA Destination Point Expired Internet Draft
Attribute for BGP

12. Advertiser BGP/IDRP Route Server RFC 1863[]

13. RCID_PATH/CLUSTER_ID BGP/IDRP Route Server RFC 1863

14. Multiprotocol Reachable Optional nontransitive, RFC 2283[]
NLRI Type code 14

15. Multiprotocol Unreachable Optional nontransitive, RFC 2283
NLRI Type code 15



16. Extended Communities draft-ramachandra-bgp-ext-communities-00.txt, "workprogress"

[ding]

what are all the conditions to be met, to become neighbors in BGP?????
Hold timers, ASN, ???????????????

[ding]

K2S,
ivaaltiki chaalu, nenu koncham vaati mee repativaraku repati varaku prep ayi osta,

[k2s]

[quote name='shakkku' timestamp='1320278566' post='3058975']
what are all the conditions to be met, to become neighbors in BGP?????
Hold timers, ASN, ???????????????
[/quote]


BGP Neighbor Negotiation

One of the basic steps of the BGP protocol is establishing sessions between BGP peers.
Without successful completion of this step, the exchange of updates will not occur. Neighbor
negotiation is based on the successful completion of a TCP transport connection, the
successful processing of the OPEN message, and periodic detection of the UPDATE or
KEEPALIVE messages.

BGP OPEN Message format

[img]http://www.h3c.com/portal/res/200706/01/20070601_108985_image002_201386_57_0.gif[/img]



Version—
A 1-byte, Version # shud match.


My Autonomous System—
A 2-byte field that indicates the AS number of the BGP speaker.
If same ASN then its iBGP else eBGP



Hold Timer—
The Hold Timer is a 2-byte. The BGP router negotiates with its neighbor to select the hold time at whichever value
is lower—its own Hold Timer or its neighbor's.



BGP Identifier—
A 4-byte, or Router ID, highest IP address. Different for different routers.



Optional Parameter Length (Opt Parm Len) —

1-byte . Indicates total length in bytes of Opt Parm field. "0" means no optinal parameters



Optional Parameters—
1 byte. example - authentication information parameter (type 1),

[k2s]

Will start the continuation in 10 mins

[k2s]

Please go thru previous lectures on BGP..

Will start the class in about 10 mins

[k2s]

Starting Today's class with " How does BGP Builds Peer Sessions: :



[img]http://i43.tinypic.com/2ngvecp.png[/img]



A neighbor connection (also referred to as a peer
connection) between two routers can be established within the same AS, in which case BGP is
called internal BGP (IBGP). Likewise, a peer connection between routers in different ASs is
referred to as external BGP (EBGP).



Upon neighbor session establishment and during the OPEN message exchange negotiation,
peer routers compare AS numbers and determine whether they are peers in the same AS or in
different ASs.



Neighbors can reach one another via some Interior Gateway Protocol (IGP), the BGP session
is established, and BGP messages are exchanged.



Most commonly for IBGP peering sessions, an Interior Gateway Protocol (IGP) or static route
can be configured to achieve IP connectivity



In some situations arise in which
external neighbors cannot be on the same physical segment. Such neighbors are logically
connected (multiple IP hops away) but not physically connected. Then, BGP drops any UPDATE message from its external BGP peer if the peer is
not physically connected, unless otherwise specified.


A BGP session formed between external BGP peers that are not physically connected is
referred to as multihop EBGP. ( RT1 & RT3)

[tom bhayya]

[k2s]

BGP Routing Process :



Routes are exchanged between
BGP peers via UPDATE messages. BGP routers receive the UPDATE messages, run some
policies or filters over the updates, and then pass the routes to other BGP peers. In case multiple routes to the same destination exist, BGP does not flood its
peers with all those routes; rather, it picks the best route and sends it.



The BGP Routing Process would involve the following components:

[img]http://i40.tinypic.com/24m6rs1.png[/img]


A pool of routes that the router receives from its peers
An Input Policy Engine that can filter the routes or manipulate their attributes
A decision process that decides which routes the router itself will use
A pool of routes that the router itself uses
An Output Policy Engine that can filter the routes or manipulate their attributes
A pool of routes that the router advertises to other peers

[k2s]

Sample Routing Environment
In the figure, AS5 receives routes from both AS1 and AS2 and originates its own routes
(172.16.10.0/24).


[img]http://i44.tinypic.com/1zwnv4l.png[/img]



By applying the engine model to AS5, you will get these results.

Routes received from peers (the routes coming from AS1 and AS2) consist of the following:
[list]
[*]192.213.1.0/24 via AS1
[*]0/0 (this is a default route) via AS1
[*]193.214.10.0/24 via AS2
[*]0/0 (this is a default route) via AS2
[*]192.213.1.0/24 via AS2
[/list]
Input Policy Engine criteria dictate the following:
[list]
[*]Do not accept default route 0/0 from AS1.
[*]Give route 192.213.1.0/24 coming from AS1 better preference than route
[*]192.213.1.0/24 coming from AS2.
[*]Accept all other routes (this will accept 193.214.10.0/24).
[*]The decision process concludes the following:
[/list]

Because 192.213.1.0/24 has better preference via AS1, I will reach 192.213.1.0/24 via AS1.
[list]
[*]I will reach 193.214.10.0/24 via AS2.
[*]I will accept 0/0 via AS2.
[/list]

Routes used by the router conclude the following:
[list]
[*]I will use 0/0 as the default from AS2.
[*]I can reach 192.213.1.0/24 via AS1.
[*]I can reach 193.214.10.0/24 via AS2.
[*]Network 172.16.10.0/24 is one of my local networks that I want to advertise.
[/list]

Output Policy Engine criteria dictate the following:
[list]
[*]Do not propagate the default route 0/0.
[*]Do not advertise 193.214.10.0/24 to AS4.
[*]Give 192.213.1.0/24 a metric of 10 when sent to AS3.
[/list]

Routes advertised to peers toward AS3 consist of the following:
[list]
[*]192.213.1.0/24 (via AS5 AS1) (this means first AS5 and then AS1) with a metric of 10
[*]172.16.10.0/24 (via AS5)
[*]193.214.10.0/24 (via AS5 AS2)
[/list]

Routes advertised to peers toward AS4 consist of the following:
[list]
[*]192.213.1.0/24 (via AS5 AS1)
[*]172.16.10.0/24 (via AS5)
[/list]

[k2s]

Ok guys , enough for today.. Lets talk more about BGP Attributes & BGP decision Making Algorithm in next class ( don ask when )

[k2s]

Today we ' ll discuss about BGP attributes....
will start in 10 mins

[k2s]

[b]BGP path attributes:[/b]
[list]
[*]Well-known mandatory
[*]Well-known discretionary
[*]Optional transitive
[*]Optional nontransitive
[/list]
Source : RFC 1771

Well-known attributes must be recognized by all BGP implementations. Some of these
attributes are mandatory and must be included in every UPDATE message. Others are
discretionary and may or may not be sent in a particular UPDATE message.

All well-known attributes must be passed along (after proper updating, if necessary) to other
BGP peers.