BGP Best Path Selection

1) Weight (highest)
2) Local Preference (highest)
3) Self Originated
4) AS_PATH
5) Origin
6) MED (highest)
7) External Route (EBGP over IBGP)
8) IGP Cost
9) RID (lowest)
10) Neighbor IP address (lowest)

BGP Case Studies @ Cisco

BGP Attributes

Well-known Mandatory
Origin
AS-Path
Next-Hop

Well-Known Discretionary
Local-Preference
Atomic aggregate

Optional Transitive
Community
Aggregator

Optional Nontransitive
MED (Multiexit Discriminator)

BGP Case Studies @ Cisco

BGP Study Notes

Path Vector protocol, uses TCP/179 as transport.
EBGP Routes have AD of 20, IBGP have 200.

BGP Syncronization Rule: Don't use or propagate a route learned by IBGP, that is not also known by another source. (an IGP)

3 Tables: BGP Forwarding, BGP Neighbor, Routing tables.

Message Types:
Open, sent to establish adj. A keepalive is sent for confirmation.
Keepalive; sent in 60 second intervals.
Update
Notification; sent in response to errors/special conditions

Neighbor States:
Idle
Connect
Open Sent
Open Confirm
Established

Attributes:
Origin
AS-Path
Next-Hop
MED
Local Pref.
Community

Commands:
Hard/soft(w/o flap) reset
# clear ip bgp {* | address}[soft [in | out]]

Send MD5 hashed password w/ every packet
# neighbor ip-address password password

BSCI Scheduled for Nov 2nd

Yep, this should be fun!
This week I'll be doing practice labs and reviews getting ready to take this monster on monday...

Multicast over Frame Relay [WIP]

ref: http://cciethebeginning.wordpress.com/tag/nbma/

DHCP serving/relaying

Anatomy of getting an address from DHCP

1. Client broadcasts DHCP DISCOVER message
2. Server replies with DHCP OFFER
3. Client asks formally for the offered address with DHCP REQUEST
4. Server acknowledges with DHCP ACK
5. Client sends out a gratuitous ARP to check if the IP address is used, if not starts using it.

Setup a DHCP Server
# ip dhcp pool {pool_name}
# network { network } { mask | prefix }
# default-router { hostname | ip }
# dns-server { hostname | ip }
# domain-name { name }
# lease { days, hours... }
etc..

* Exclude addresses from pools with # ip dhcp exclude-address {low_address} {high_address}
** Addresses are always assigned on the interface that has an IP address in the same subnet as the pool.

Acting as DHCP Relay
Use following interface configuration command to forward certain broadcasts.

R1 (config-if) # ip help-address {destination server}

Troubleshooting
# sh ip dhcp binding
# clear ip dhcp binding
# sh ip dhcp pool
# sh ip dhcp server statistics

IS-IS Hello/Hold Timers

Default Hello timer is 10 seconds, and the default hello multiplier is 3, so Hold time is 30 seconds.
On broadcast links the DIS will be 3 times faster meaning a Hello Timer of 3.3 seconds.

In broadcast links, Hellos are sent with a multicast MAC address;
an IIH packet is sent for each Level the router belongs to.

In point-to-point links a single IIH packet is used which has a flag denoting if it's Level-1,2 or both.
Hello packets are sent to the unicast addresses.

IS-IS Authentication

1-) Clear text:

# router isis
# isis password MyPaSS

2-) Area password:

# router isis
# area-password YesAnAreaPass

3-) Domain password:

# router isis
# domain-password ThisWouldBeEasy

4-) MD5 Authentication:

Use it either under an interface or the whole router process; first create your key-chain. (Eg: keyISIS)

# interface s1/0
# isis authentication key-chain keyISIS
# isis authentication mode md5

or under router process

# router isis
# isis authentication key-chain keyISIS
# isis authentication mode md5

you can also limit it to level-1 or level-2 and send-only

# isis authentication mode md5 { level-1 | level-2 }
# isis authentication send-only { level-1 | level-2 }

IS-IS Pseudonode and DIS (Designated IS)

In IS-IS a broadcast link itself is modeled as a pseudo-node that connects all attached routers to a star topology.
The pseudo-node is represented by the DIS (Designated router)



On broadcast type links a DIS is elected for both Level-1 and Level-2, if they exist.
A router with highest priority or highest SNPA (MAC,DLCI,..) address is selected as DIS.
Default priority is 64. (can be between 0-127)
DIS election can be preempted, any priority change will take effect immediately.

There is no backup DIS (unlike OSPF) and all routers in a LAN establish adjacencies with each other and the DIS.

The DIS creates and maintains the pseudo-node LSP.
This LSP contains the adjacent ISs, just like the network lsa in OSPF.

EIGRP Stub Router

Stub routers in EIGRP will only send limited information to their ONLY neighbor, a core (EIGRP) router.
This way the router will minimize memory and processor utilization.
Also helps speeding up convergence because a stub router answers to queries as inaccessible, thus limiting the query range and preventing SIA situations.

Syntax:
eigrp stub [receive-only | connected | redistributed | static | summary]

Distance command

Filter and change AD of routes before they enter the RIB.

1-) Protocol independent "distance" command:
distance AD advertising_router_ip wildcard access-list

You can have multiple distance commands.
Also a default distance that will apply to any routes not defined in another "distance" command.

2-) Protocol dependent:

With this you can change the AD of an external/internal route for EIGRP, external/inter-area/intra-area route for OSPF and so on.

Eg:
distance ospf external 125 (sets all the external OSPF routes that are learned with and AD of 125)

OSPF Network Types

OSPF Communication:
Multicast 224.0.0.5: All OSPF Neighbors listen
224.0.0.6: Only DR and BDR listen

OSPF Network Types:

RIP Lab advises from a CCIE

These quick-and-dirty notes are not from me, I came across a post on a blog, and thought it could be useful..

So, taking note for future reference..

Opening Move:
————-
conf t
router rip
ver 2
no auto
pass def

do sh ip int br
network
no pass

!Broadcast v2 update:
———————
(config-if)#ip rip v2-broadcast

!Unicast updates:
—————–
1- send unicast updates
(config-router)#neighbor A.B.C.D “Neighbor address”
2- stop broadcast/multicast updates
passiv

Differet subnets:
—————–
(config-router)#NO validate-update-source

!check split horizon

Show commds:
————
Sh ip protocols
Routing Information Sources:
Gateway Distance Last Update

Killing the Route:
——————
1- Distribute list
2- offset list (poison the metric)
3- admin distance (poison the distance)

Reference