BSCI Notes

The enterprise composite model is broken up into three large pieces:
• Enterprise campus
• Enterprise edge
• Service provider edge

Distance vector(thier routing table to  thier neibhors) and link state routing protocols(advertising
a list of their neighbors and the networks attached to thier neighbors and run SPF algorithem.

Protocol Technique
RIP Distance Vector
RIPv2 Distance Vector
EIGRP Distance Vector
OSPF Link State
IS-IS Link State
BGP Path Vector

VLSM-variable length subnet masks
EIGRP is cisco proprietary protocol.

RIP and IGRP have to use periodic transmission as both a routing adver and keepalive message.
Modern routing protocols are only sent update functions and seperate keepalives.

Class A: 0-127, Class B: 128-191, Class C:192-223, D: 240-255

Eigrp is a distance vector protocol
Uses DUAL(diffusing update algorith convergence algorith. this identifies the procedure used to sort the list of available paths and select best paths and feasible fail-over routes.
This is also hybrid protocol.
its use over a NBMA(nonbroadcast multiaccess WAN environment)
EIGRP produces ‘reliable updates’ by identifying its packets using IP protocol 88.
The following five packets is used
 -Hello – Identifies neighbors. hellos are sent as periodic multicasts and are not acl directly.
 -Update – Advertises routes. Updates are sent as multicast only there is a change.
 -ACK- ack receipt of an update.
 -Query – Used to ask about routes for which the previous best path has been lost. If
an update indicates that a path is down then multicast queries are used to ask other
neighbors if they still have a path. If the querier does not receive a reply from each of
its neighbors then it repeats the query as a unicast to each unresponsive neighbor until
it either gets a reply or gives up after sixteen tries

 -Reply – Used to answer a query. Each neighbor responds to the query with a unicast reply indicating an alternative path or the fact that it does not have a path.

Neighbor Discovery and Recovery:

 1. First hellos are used to build a list of neighbors
 2. Second hellos indicate that the neighbor is still alive.
 3. hold time – missing long period of time
 4. after 16 attemtps the neighbor is removed .
 5. Advertisements are multicast. repplys are unicast.
 6. metric = 256*(K1 * bandwidth + K2*bandwidth                   K5
                                   ————- + K3 * delay)————-
                                      256 load                 reliability + K4
 7. Eigrp selects path based on fastest path.
 8. It uses K- values to balance bandwidth and delay. K-values are constant.
 9. Bandwidth is defined as 107 kbps divided by the slowest link along the path
10. Load and reliability are 8-bit calculated values based on the performance of the link
11. Delay is a constant value on every interface type, and is stored in terms of
 microseconds. For example, serial links have a delay of 20,000 microseconds and
 Ethernet lines have a delay of 1000 microseconds. EIGRP uses the sum of all delays
 along the path, in tens of microseconds
12. By default, K1=K3=1 and K2=K4=K5=0
13. Routers will not become EIGRP neighbors unless they share K-values
14. the cost from the neighbor to the destination is called the ‘advertised distance’
15. the cost from the source to destination called the feasible distance.
16. The neighbor with the best path is referred to as the successor
17. Neighbors that meet the feasibility requirement are called feasible successors
18. Recursive queries can loop without being resolved, forcing the router to time-out the query.
 This situation is known as stuck in active (SIA).
19. EIGRP uses split-horizon, which says that a router should not advertise a network on the
 link from which it learned about the network
20. Some packets are sent reliably using real-time protocol(RTP).
21. Updates are sent using a reliable multicast. The address is the reversed class D address,
22. When the neighbor receives a multicast, it acknowledges receipt of the packet
 with an unreliable unicast
23. EIGRP builds three tables, A neighbor tables, a topology tables, IP routing table.
24. The holdtime, by default, is three times the Hello timer. Hello timer on a LAN is set to 15 secs.
25. ON DS1(1.5 Mbps) or slower WAN links the hello timer is 60 secs and holdtime is 180secs.

1. Bgp neighbors are called peers and must be predefined.
2. There are 4 bgp message types, open, keepalive, update, notification.
3. When a BGP process starts, it creates and maintains connections between peers on TCP 179, using BGP Open messages
4. These sessions are maintained by periodic keepalive messages, and peer information is kept in a separate neighbor table
5. When neighborship is first established, BGP routers exchange their complete routing tables using update messages
6. ROuting with bgp involves three tables, neighbor, bgp and ip routing table.
7. Redundant Internet connectivity is referred to as multihoming
8. Multihoming might involve more than one connection to the same ISP or connections to separate ISPs
9. BGP cycles through five states as it runs, idle(searching for neighbors, connect(TCP handshake complete with neighbor
   open sent(bgp open message has been sent), open confirm(response received), Established(bgp neighborship is established.
10.bgp is an enhanced path vector protocol that supports VSLM, CIDR and summarization.


This is my technial blog. You can find here some technical topics that are useful in various technical fields.  Presently I have been working with a telecomm company.  I deal with various issue in work place. I dont remember all the things which I deal so this is the place I keep my thoughts.  Please feel free to leave your comments if you have any on anything.