14th Lecture - Networking

[robo]

[quote name='k2s' timestamp='1320181237' post='3054687']
Please download the book :-

[url="http://rapidshare.com/files/59610919/BGP_Internet_Routing_Architecture.pdf"]http://rapidshare.co...rchitecture.pdf[/url]
[/quote]

chesi petu grrrr

[GUNTUR2US]

but precisely about what?

[CaliStar]

[quote name='GUNTUR2US' timestamp='1320182031' post='3054757']
but precisely about what?
[/quote]

BGP routing protocol mama....

[k2s]

Intru:


The Border Gateway Protocol (BGP) has gone through several phases and improvements
since its original version, BGP-1, in 1989. BGP-4 deployment began in 1993. It is the first
BGP version that handles aggregation (classless interdomain routing [CIDR]) and
supernetting


BGP assumes that routing within an autonomous system is done via an intra-autonomous system routing protocol
(Interior Gateway Protocol [IGP]).


BGP constructs a graph of autonomous systems
based on the information exchanged between BGP routers. This directed graph environment is
sometimes referred to as a tree. As far as BGP is concerned, the whole Internet is a graph of
ASs, with each AS identified by a unique AS number. Connections between two ASs together
form a path, and the collection of path information forms a route to reach a specific
destination.




How BGP Works ?

BGP is a path vector protocol used to carry routing information between autonomous systems.
BGP uses TCP as its transport protocol (port 179). This ensures that all the transport
reliability (such as retransmission) is taken care of by TCP and does not need to be
implemented in BGP.



Two BGP
speakers that form a TCP connection between one another for the purpose of exchanging
routing information are referred to as neighbors or peers.

[k2s]

Peer routers exchange open messages to determine the connection parameters.

[k2s]

BGP Finite state Machine:

[img]http://2.bp.blogspot.com/_-UuUNCTEs4A/TVEj6AEMfWI/AAAAAAAAACw/2_A0PZ82DwY/s640/paste.jpg[/img]
We ' ll learn about each state ..

[k2s]

Idle—
This is the first stage of the connection. BGP is waiting for a Start event, which is
initiated by an operator or the BGP system. An administrator establishing a BGP
session through router configuration or resetting an already existing session usually
causes a Start event. After the Start event, BGP initializes its resources, resets a

ConnectRetry timer, initiates a TCP transport connection, and starts listening for a
connection that may be initiated by a remote peer. BGP then transitions to a Connect
state. In case of errors, BGP falls back to the Idle state.

[riddle]

Nenu intiki jump avuthunna.. oka 1 1/2 hr lo join avutha.....

[k2s]

[quote name='riddle' timestamp='1320182517' post='3054821']
Nenu intiki jump avuthunna.. oka 1 1/2 hr lo join avutha.....
[/quote]

k

[k2s]

Connect—
BGP is waiting for the transport protocol connection to be completed. If the TCP
transport connection is successful, the state transitions to OpenSent (this is where the
OPEN message is sent). If the transport connection is unsuccessful, the state
transitions to Active. If the ConnectRetry timer expires, the state remains in the
Connect stage, the timer is reset, and a transport connection is initiated. In case of any
other event (initiated by system or operator), the state goes back to Idle.

[k2s]

Active—
BGP tries to acquire a peer by initiating a transport protocol connection. If the
transport connection is established, it transitions to OpenSent (an OPEN message is
sent). If the ConnectRetry timer expires, BGP restarts the ConnectRetry timer and falls
back to the Connect state. In addition, BGP continues to listen for a connection that
might be initiated from another peer. The state might go back to Idle in case of other
events, such as a Stop event initiated by the system or the operator.

[k2s]

OpenSent—
BGP is waiting for an OPEN message from its peer. The OPEN message is checked
for correctness. In case of errors, such as a bad version number or an unacceptable AS,
the system sends an error NOTIFICATION message and goes back to Idle. If there are
no errors, BGP starts sending KEEPALIVE messages and resets the KEEPALIVE
timer. At this stage, the hold time is negotiated, and the smaller value is taken. In case
the negotiated hold time is 0, the Hold Timer and the KEEPALIVE timer are not
restarted.
At the OpenSent state, the BGP recognizes, by comparing its AS number to the AS
number of its peer, whether the peer belongs to the same AS (Internal BGP) or to a
different AS (External BGP).
When a TCP transport disconnect is detected, the state falls back to the Active state.

[k2s]

OpenConfirm—
BGP waits for a KEEPALIVE message. If a KEEPALIVE is received, the state goes
to Established, and the neighbor negotiation is complete. If the system receives a
KEEPALIVE message, it restarts the Hold Timer (assuming that the negotiated Hold
Time is not 0). If a NOTIFICATION message is received, the state falls back to the
Idle state. The system sends periodic KEEPALIVE messages at the rate set by the
KEEPALIVE timer. In case of any transport disconnect notification or in response to
any stop event (initiated by the system or the operator), the state falls back to Idle. In
response to any other event, the system sends a NOTIFICATION message with an
FSM (Finite State Machine) error code and returns to the Idle state.

[k2s]

Established—
This is the final stage in the neighbor negotiation. At this stage, BGP starts exchanging
UPDATE packets with its peers. Assuming that it is nonzero, the Hold Timer restarts
at the receipt of an UPDATE or KEEPALIVE message. If the system receives any
NOTIFICATION message (if an error has occurred), the state falls back to Idle.
The UPDATE messages are checked for errors, such as missing attributes, duplicate
attributes, and so on. If errors are found, a NOTIFICATION message is sent to the
peer, and the state falls back to Idle. If the Hold Timer expires, or a disconnect
notification is received from the transport protocol, or a Stop event is received, or in
response to any other event, the system falls back to the Idle state.

[riddle]

Endhi baa apesavu...