Jeff Doyle -Vol 1: Chapter 7 Notes, EIGRP

IGRP: AD=100; IP Protocol 9; update 90s, invalidation = 3×90, holddown = invalidation+10, Flush = 7×90

Metric = {k1*BWIGRP + k2* BWIGRP /256-LOAD+k3*DLYIGRP} * k5/ (Reliability+k4)

Typically metric = BW_IGRP + DLY_IGRP; BW_IGRP = 10^7/BW in Kbps, DLY_IGRP = Delay in 10’s of microseconds. Unreachable DLY_IGRP = FFFFFF = 167.8s

router igrp 1
metric weights <tos> k1 k2 k3 k4 k5

EIGRP: AD=90, default 100 hops, max 255 – n/w diameter, not a metric. Hello interval = 5s (on b/c and p-to-p links) 60s otherwise. Holdtime=3xHello. Multicast 224.0.0.10. IP protocol88  Metric = 256*IGRP metric.
Components of EIGRP:

Protocol dependant modules: IP/IPX/Appletalk.

DUAL

Neighbor Discovery/Recovery

Reliable Transport Protocol

EIGRP automatically redistributes: IPX -> IPX RIP/NLSP, Appletalk -> RTMP, IP -> IGRP (same AS#)
RTP: Hellos – unreliable m/c, ACK – unreliable unicast, UPDATES – reliable, non-periodic, bound, partial, m/c or u/c. QUERIES – m/c or u/c, reliable, REPLIES – u/c reliable, REQUESTS – unused
m/c flowtimer ……….. expires -> unicast (16 times)

Neighbor Discovery/Recovery: interface:

ip hello-interval eigrp <>
ip hold-time eigrp <>
sh ip eigrp neighbors

DUAL: Uses low-level protocols (RTP+ND/R) to :

- Detect new/loss of neighbors
- Make sure the messages are valid
- Make sure the updates are processed sequentially and correctly

1. Establish adjacencies
2. Exchange Updates
3. Calculate Metrics

R1———————R2———————-R3—

\\\\\\\\\\\\\\\\\\\\\|————————| AD

|————————————————–| FD

Feasibility Condition: AD < FD. If FC is met, the neighbor becomes a Feasible Successor
Topological table contains: Every destination, FS, Successor, FD, neighbor’s AD, i/f.
show ip eigrp topology

Route is PASSIVE <—– INPUT EVENT*

|

|

New FS with lower metric — > add

(or)

New FD < old FD — > update FD

(or)

New Distance — > Send update

|

|

If no FS, route = ACTIVE à initiate Diffusing Computation

| | |

Query Query Query (set reply flag ‘r’)

|

If a neighbor has a FS, it sends a reply; else it sends a Query and goes ACTIVE

|

SIA if no reply is received from all neighbors within 3 mins

*INPUT EVENTS: Cost change of directly connected link, status change of link, update, query or reply
ACTIVE timer can be changed from 3 mins by: router eigrp 1, timers active-time <>

If no FS is discovered from the replies, the FD is set to infinity so that any non-infinite metric is added as FS.

EIGRP Header:

Version	Op Code	Checksum
Flags
Sequence #
Ack #
AS #
TLVs

Flag=1 => new neighbor, first set of routes.

TLVs: K values, load, reliability, AS#, next-hop, External R.P, metric.

CIDR: address aggregation by IANA

EIGRP performs unequal load balancing using VARIANCE: router eigrp 15; var 5
Maximum paths: 1->16, default 4.
*!* Implicit default command: traffic-shape balanced. If only the least cost path needs to be used, but all other routes need to be injected into the routing table, use traffic-shape min
Multiple EIGRP instances: to prevent inter-instance updates, define the i/f in AS1 as a passive i/f for the other AS etc. or use very specific wildcard bits so the exact n/w is matched. router eigrp 10; network 172.20.15.0 0.0.0.255
router eigrp 10; no auto-summary – stops auto-summarization at the n/w boundary
Stub: updates contain only directly connected, static, summary or redistributed networks. router eigrp 10; eigrp stub {connected|static|direct|summary|receive-only}
show eigrp neighbor detail – indicates ‘stub’
To summarize: interface: ip summary-address eigrp 10 172.0.0.0 255.0.0.0
Authentication: same as RIPv2 key-chain; Supports only MD5
i/f: ip authentication key-chain eigrp 10 KC.
Troubleshooting: debug eigrp packets, debug eigrp neighbor
SIA: IOS 12.2[4.1] onwards have a SIA retransmit timer. Enables a route to be active for upto 6 mins before going SIA

|——————————||——————————||——————————————–|

0 90 180 360

Q0,R0 Q1,R1 Q3,R3 SIA

As long as a neighbor responds to a query, the SIA re-tx and Active timers are reset (3 attempts)
SIA causes: low b/w, congestion, resource issues (CPU/memory). EIGRP uses a max of 50% of the b/w by default. Interface: ip bandwidth-percent eigrp 200 (eg 56k link)

Jeff Doyle -Vol 1: Chapter 6 Notes, RIPv2/RIPng

http://ccieyatra.wordpress.com/2008/01/28/5/

Jeff Doyle -Vol 1: Chapter 5 Notes, RIP

RIP: UDP 520; update = 30s, invalidation = 6×30, holddown = 6×30, flush = invalidation +120s (Cisco uses +60s)
router rip
timers basic <update> <invalid> <holddown> < flush>
Changing the timer on any one router affects every neighbor it talks to => affects RIP domain
Triggered update: Only over serial links, only when changes occur. Timer 1-5s. Configured at both ends. (RIP timer expiry is observed in debugs)
debug ip rip trigger
interface se1/0
ip rip triggered.

Max message size =512 bytes.
Command: 1= Request, 2= response, AFID = 2 for IP. (When a full table is requested, AFID=0, IP=0.0.0.0 & metric=16)

Classful Routing: If the n/w does not match the subnet of it’s i/f, RIP will treat is as a major n/w.
Passive if: router rip; passive interface se1/0 – > no updates are sent.
Neighbor: Default updates are b/c. router rip, neighbor <ip> will force unicast
Secondary IP address: To connect two discontigous n/ws, configure a secondary IP address with same mask and same classful n/w (for eg. 10.75.3.1 255.255.252.0 to connect 10.55.3.1 255.255.252.0)
Offset-List: Used to influence RIP metrics.
access-list 1 permit 10.33.0.0 0.0.0.0 (mask matches the n/w exactly)
router rip
offset-list 1 in 3 se 1/0 (add a metric of 3 to traffic matching ACL 1, incoming on se1/0)
If no i/f is specified, any traffic matching the acl on any i/f is affected.
If no ACL, all traffic through that i/f is affected

Troubleshooting: If there is a slow – fast neighbor combination and the slow router cant keep up with the RIP updates; on the faster router:
router rip
output-delay <8-50ms>

Jeff Doyle -Vol 1: Chapter 4 Notes, Dynamic Routing Protocols

Distance vector: RIP v1&2, IGRP, EIGRP, DEC’s DNA Phase IV, Appletalk RTMP

Common characteristics: Periodic updates (except EIGRP), neighbors, b/c updates (except RIPv2 and EIGRP), Full table

Link State: OSPF, ISIS, DEC’s DNA Phase V, NLSP. Uses Hello packets.

- LSA (not full routing table) use Seq and ACK #s.

Sequencing Algorithms:
Linear -> 1—————- X (where X is a very large #). Issue: router restart will reinitialize sequencing. Soln: Neighbor on receipt of a lower seq # sends its LSA (contains the last seq#) to that router. ISIS

Circular Sequencing. Eliminates need for neighbor to send an LSA to reinitialize sequencing. Cyclic 0 to n. Uses: if a>b; a-b < or = n/2 => a is latest. If a<b, b-a > n/2 => a is latest.

Lollipop Shaped: hybrid. (-N+1) to 0 : Linear, 0 to (N-2) is circular. OSPFv1
Current version of OSPF(v2) uses a Linear model (-N+1)——–0——-(N-2)

Aging: Set to 1 when LSA is created and incremented as a function of time at each router. It defines the MaxAgeDiff. If 2 LSAs with same seq# are received and if the difference in their ages is greater than MaxAgeDiff, the newer one is added.

Link State Database = Router Link Information + Stub n/w information
Dijkstra’s Algorithm: Database Tree <- Candidate <- Link state

- Router builds a SPF tree by first adding itself as a root node.
- It then creates a list of all directly connected neighbors and associated costs.
- Lowest cost link to a neighbor becomes a branch.
- This router’s neighbors are then added to the list
- The list is checked for duplicates and higher cost paths to dupes are dropped
- The lowest cost router is added to the tree and its neighbors are added to the list
- Process is repeated

Stub info is then added and the route is injected into the routing table.

Link State Routing Protocol Concerns: High CPU, B/w, memory – mitigated by areas.

EGPs: BGP, EGP, ISO’s IDRP, NLSP Level3 Routing.

Jeff Doyle -Vol 1: Chapter 3 Notes, Static Routing basics

ip route 10.10.1.0 255.255.255.0 fa0/0 10.200.1.1 – combination of i/f and next hop
ipv6 static routing:
(config)#ipv6 unicast-routing
interface fa0/0
ipv6 enable
ipv6 address fec0:0:0:3::/64 eui-64
IPv6 show commands:
show cdp neighbor details
show ipv6 interface fa0/0
show ipv6 route -> L indicates locally connected
If global IP addresses are re-numbered, link-local addresses remain the same. If the router has to be replaced, routing has to be reconfigured (if routes point to link-local addresses)
IPv6 never responds to PROXY-ARP

Alternate routes: static routes with a higher cost (influences the AD)

Load sharing: per packet/ per destination. Per packet is obviously a more ‘fair’ load-balance but may cause packets to arrive out of order. This maybe unacceptable for real-time applications like VoIP.

CEF: uses 2 tables FIB (L3 derived from routing table) and Adjacency table (L2 from ARP and NS). The tables are built even before the first packet needs to be routed.
Default : per destination (src & dest)
sh ip cef; sh ipv6 cef
at the interface: ip load-sharing per-packet

Ingress i/f

egress i/f

s/w ing method

CEFCEF Process Process Fast Fast

ProcessFast CEF Fast CEF Process

CEFCEF Fast Fast Fast Process

Fast Switching: Only done per-destination. 1^st packet -> route table lookup, select egress i/f. -> L2 encap. Store this info in a cache (F.S cache). Subsequent packets use the cache.

Process Switching: IPv6 default. Only process s/w’ed packets show up in debug ip packet. Sometimes even if CEF is enabled, the packets are process sw’ed. Eg: access-list logging.

Recursive route lookup: when the gateway for a route is not directly reachable.