Notes on Aaron's Worthless Words

Redistribution Notes - AD Manipulation

Wed, 22 Jun 2011 00:00:00 +0000

Manipulating administrative distance (AD) is another way to help with a mutual redistribution scenario.
EIGRPs has different ADs for internal and external (redistributed) routes
OSPF and RIP have the same AD no matter where the route orginated.
This means that routes redistributed into OSPF may be used instead of a local RIP route.
- AD 110 (OSPF) beats 120 (RIP) every time.
The distance subcommand allows you to change the AD on specific routes from specific neighbors.
This example changes the AD of the route to 10.0.0.0/16 advertised from 1.1.1.1 to 121.
- This will make this router prefer a RIP route to the same destination.

ip access-list standard RIP-ROUTES
 permit 10.0.0.0 0.255.255.0
!
router ospf 1
 distance 121 1.1.1.1 0.0.0.0 RIP-ROUTES

– Corrections are encouraged.

Redistribution Notes - Tagging

Mon, 20 Jun 2011 00:00:00 +0000

Tagging provides a way to mark common or similar routes to manipulate later.
In redistribution scenarios with mutual redistribution on two different routers, any routes that gets redistributed from one route process to another are tagged.
- When the other router sees those tags on the route, that route to keep from adding non-optimal routes to its routing table.
Tags can also be used to do other manipulation such as setting higher metrics or changing ADs.

OSPF

BGP Notes - Backdoor Routes

Sat, 11 Jun 2011 00:00:00 +0000

The fact that eBGP has an AD of 20 can be a problem.
- You may have a very short path via EIGRP (or OSPF or RIP or whatever other IGP), but the longer eBGP path will be preferred.
For God’s sake, do not lower the AD of EIGRP! Havoc will ensue.
Using backdoor routes causes eBGP routes to have an AD of 200.
- Allows the shorter-path IGP routes to be added to the routing table.

router bgp 123
 network 1.1.1.0 backdoor

-—-

BGP Notes - Synchronization

Sat, 11 Jun 2011 00:00:00 +0000

With synchronization on, route must be synchronized to an IGP in order for that routes to be able to be voted ‘best" by BGP.
- That means the exact route must already be in the routing table via an IGP.
- Static routes don’t count.
- This is traditionally accomplished by redistributing BGP routes into an IGP.
- With today’s Internet prefix count over 350k, this may not be such a good idea in some situations.
- Synchronization is off by default.
Synchronization prevents black hole routes from being advertised via iBGP.
- Unless every router is participating in iBGP, there’s no guarantee that any one router will have a route to NEXT_HOP.
Synchronization also prevents a router from advertising the black hole to an eBGP neighbor.
- You don’t want to tell the world you have a path to a prefix when you really have a !N.
Synchronization can be safely disabled with the use of route reflectors or confederations.

-—-

BGP Notes - Authentication

Fri, 10 Jun 2011 00:00:00 +0000

Corrections welcome.

It’s simple as pie to enable MD5 auth to a BGP peer.

R102(config-router)#neigh 192.0.2.101 pass MYKEY

BGP Notes - Path Decision

Thu, 09 Jun 2011 00:00:00 +0000

This is required blogging…and reading for that matter. A good chunk of this is taken from my CCNP posts from last year. Corrections, please.

-—-

How does a BGP router decide which BGP route is the best?

Next-hop : Does the router have a route to the next-hop?

Weight : This is a numeric value where bigger is better. Weight is not passed onto other peers and is a Cisco proprietary feature.

BGP Notes - Path Attribute Categories

Wed, 08 Jun 2011 00:00:00 +0000

Make my corrections! Please!

Well-known mandatory : These PAs must be recognized by all BGP routers and passed along to other peers.

Well-known discretionary : These PAs do not need to be in every update, but they must be recognized by all BGP routers.

Optional transitive : These PAs don’t have to be recognized but they must be passed along to other BGP peers if they are present in an update.

BGP Notes - Message Types

Tue, 07 Jun 2011 00:00:00 +0000

Corrigeme, por favor.

Open : When a neighbor is configured, the router sends an open to that neighbor to get the ball rolling.

Destination:  The neighbor's configured IP
Important fields:
  My AS

Update : The routing information

Destination:  The neighbor's configured IP
Important fields:
  Advertised network Klonopin Online
  Path attributes

Keepalive : Sent every 60 seconds by default

Destination:  The neighbor's configured IP
Important fields:
  Nothing, really

Notification : When something is amiss, the router sends a notification message. The receiver then closes the connection.

BGP Notes - Neighbor States

Tue, 07 Jun 2011 00:00:00 +0000

Corrections appreciated.

Idle : There is no relationship, but the router sends out a TCP SYN to the neighbor to get the ball rolling.

Idle (admin) : The neighbor is admined down.

Connect : The router is waiting for the TCP connection to finish. If the TCP connection finishes, the router sends an open and transitions to OpenSent. If it times out, it transitions to Active.

Active : The router tries Cialis to initiate a TCP connection. If the TCP connection finishes, the router sends an open and transitions to OpenSent.

EIGRP Notes - Route Filtering

Tue, 07 Jun 2011 00:00:00 +0000

As always, correction are encouraged.

You can configure an EIGRP router to filter routes from being advertised or from being accepted.

Objective: Filter out the route to 10.0.254.1/32 from being advertised to the rest of the network via EIGRP.

ip prefix-list PRE1 deny 10.0.254.1/32
ip prefix-list PRE1 permit 0.0.0.0/0 le 32
!
router eigrp 1
 distribute-list prefix PRE1 out

-- OR --

ip access-list standard ACL1
 deny 10.0.254.1 0.0.0.255
 permit any
!
router eigrp 1
 distribute-list ACL1 out

EIGRP Notes - Unequal Cost Path Load Balancing

Mon, 06 Jun 2011 00:00:00 +0000

Per the standard rules, please correct anything that’s wrong.

One of EIGRP’s big features is the ability to use unequal cost paths for load balancing. This is done with the variance command.

variance : A multiplier used to calculate which feasible successors can be used as active routes. The router takes integer and multiplies it by the successor’s feasible distance, and any FS with a an FD less than this new number gets submitted to the routing table manager.

IIUC Notes - Inbound Dial Peer Matching

Wed, 19 Jan 2011 00:00:00 +0000

More IIUC notes. As always, feel free to correct as needed.

To match inbound calls to a dial peer, CME (and CUCM?) uses the following steps.

Match DNIS (the dialed number) with the incoming called-address config in the dial peer
Match the ANI (the calling number or caller ID) with the answer-address config in the dial peer
Match the ANI with the destination-pattern config in the dial peer
Match an incoming POTS call to the port config in the dial peer
Match dial peer 0

Matching dial peer 0 is bad, and it took me an inquiry on Twitter and a buddy to realize why. Here are a few highlights as to why. I believe the full scope of the badness of dial peer 0 is really beyond the IIUC exam.

IIUC Notes - Wildcards for Destination Patterns

Tue, 18 Jan 2011 00:00:00 +0000

As always, feel free to correct anything that needs correcting or add anything that needs adding. There is a lot more to the full definition of wildcards, but these are the basics. Note to *nix guys: This isn’t regex as you understand it. Yes, the use of curly braces would be nice, but we don’t get that here.

T: Represents anywhere from 0 to 32 digits

destination-patter 9T <- matches a 9 followed by 0 - 32 other digits

CME Exercise #1

Thu, 07 Oct 2010 00:00:00 +0000

I tried something like this earlier this year with STP. It got rave reviews (from my mother), so I figured I try it again.

Below is a list of requirements for configuring a router as a call processor. In a lab or in your head, configure the router to support the features as listed. This isn’t a contest or anything like that. If you get it right, a virtual thumbs up is all I can afford to give you. There are some licensing issues for running this stuff in GNS3/dynamips, so I can’t help you out on that. I’ll just hint that GNS3 and dynamips will bind to real networks and that copies of a compatible IP softphone are available.

IIUC Notes - Voice Ports and Dial Peers

Mon, 04 Oct 2010 00:00:00 +0000

More of my IIUC study notes. As always, feel free to correct. I really need to have a real post, don’t I?

show voice port summary

Shows the voice ports available for use

R1#show voice port summary
                                          IN       OUT
PORT           CH   SIG-TYPE   ADMIN OPER STATUS   STATUS   EC
============== == ============ ===== ==== ======== ======== ==
50/0/1         1      efxs     up    up   on-hook  idle     y
50/0/1         2      efxs     up    up   on-hook  idle     y
50/0/2         1      efxs     up    up   on-hook  idle     y
50/0/2         2      efxs     up    up   on-hook  idle     y
50/0/3         1      efxs     up    up   on-hook  idle     y
50/0/4         1      efxs     up    up   on-hook  idle     y
50/0/5         1      efxs     up    up   on-hook  idle     y

An ephone-dn shows up as efxs, so all these are ephone-dns.
Channels are numbered 0-23; timeslots are numbered 1-24

FXS Ports

IIUC Notes - More Phone Features

Sat, 02 Oct 2010 00:00:00 +0000

Here are some more notes from my IIUC studies. As always, corrections requested.

Paging

Broadcasts messages to a group for a one-way communication
Paging groups are used to limit which phones get the broadcast
Paging can be unicast or multicast
- Unicast groups limited to 10 members
- Multicast requires mcast support on the network
Paging configurations can be unicast, multicast, or multiple-group

! Unicast Paging
! When 1044 is dialed, ephone 1 is paged
R1(config)#ephone-dn 44
R1(config-ephone-dn)#number 1044
R1(config-ephone-dn)#paging
R1(config-ephone-dn)#exit
R1(config)#ephone 1
R1(config-ephone)#paging-dn 44

IIUC Notes - Phone Features

Fri, 01 Oct 2010 00:00:00 +0000

Here are some more notes from my IIUC studies. As always, corrections requested.

Local Directory

Allows users to look up names
Allows names to show up when dialing or receiving a call
Most phones have a directory button; some have a menu options for the directory

R1(config)#ephone-dn 1
R1(config-ephone-dn)#name Roger Smith

Directory entries can be added manually

R1(config-telephony)#directory entry 1 1700 Corporate Fax
R1(config-telephony)#directory entry 2 1701 HR Fax

By default, sorting is done alphabetically by first name.
Sorting can be changed

R1(config-telephony)#directory last-name-first

IIUC Notes - Getting Phones on the LAN

Thu, 30 Sep 2010 00:00:00 +0000

More study notes. Correct if wrong, though I hope I get some of it right since I already since I’m an R&S guy. :$

**Switchport Configuration
**

switchport mode access: This config makes the port an access port that carries the primary and voice VLAN traffic
switchport mode trunk: This config akes the port a trunk unconditionally, but it will still send DTP messages
switchport nonegotiate: This config keeps the port from sending DTP messages.
switchport mode dynamic auto: If the port receives DTP messages, it will become a trunk. If not, it will be an access port.
switchport mode dynamic desirable: The port actively sends DTP messages trying to become a trunk. This is the default configuration on a Cisco switch.

Cisco IP Phone Boot Process

IIUC Notes - Assigning Ephone-dns to Ephone Buttons

Thu, 23 Sep 2010 00:00:00 +0000

These are some of my notes on my IIUC studies. Since I am a novice as voice stuff, please let me know what I get wrong.

An ephone is a representation of a phone. It’s basically a structure of features that a phone will have.

Configuration in CME:

R1(config)#ephone 34 <– This is just a tag and has nothing to do with an extension or phone
R1(config-ephone)#mac-address 1111.2222.3333 <– Assigns this ephone to the phone with that MAC address

IIUC Notes - Powering Cisco Phones

Tue, 21 Sep 2010 00:00:00 +0000

Feel free to correct anything that is wrong or incomplete.

Power over Ethernet (PoE)
- Can provide power to a Cisco phone, access point, security camera, etc., through the network cabling, eliminating the need to plug the phone into the wall for power.
- Generic term for providing power on the Ethernet cable
- Provides centralized power that can be put on a UPS
- Allows devices to be located away from power outlets
- Removes cabling clutter at the user’s desk
- Can be provided through PoE-enabled switches, power panels or inline couplers (power injectors)
- Oversubscription is common
  - If every device on a switch asks for full power, the switch may not be able to handle the load.
- Of course, devices can be powered with a power brick at the desk
802.3af

IIUC Notes - VoIP Structures

Tue, 21 Sep 2010 00:00:00 +0000

Feel free to correct. No need to sugar-coat it; I’m pretty new at this stuff. :)

Advantages of VoIP
- Reduces costs of communications: Eliminates/reduces long distance and international call tolls
- Reduces costs of cabling: No need for second network of phone lines
- Integrates all voice into one large network: All your remote offices can be implemented/maintained/controlled centrally
- Provides mobility: Moves, adds, and changes (MACs) are (nearly) eliminated since your phone is just a network node
- Allows use of IP Softphones
- Unifies emails, voice mails, and faxes: All these can be treated as a single box for user messages
- Increases productivity: Ringing multiple devices at the same time eliminates phone tag. <— pushing it, eh?
- Enhances communications: Applications can be launched/updated from a voice call through application servers
- Provides open, compatible standards: You can connect different vendor devices into the same VoIP network. <— I’ve never seen that happen
Cisco VoIP Structure

IIUC Notes - Old School Voice Stuff

Wed, 08 Sep 2010 00:00:00 +0000

These are the notes I’ve taken as I read through the study materials. Feel free to correct anything you see.

Analog phone signaling
- Misc
  - Ground = positive = tip
  - Battery = negative = ring
  - Signaling uses specific frequencies for specific events
- Loop start signaling
  - When a circuit in the phone is completed (i.e., you take it off-hook), the CO detects it and provides services.
  - Susceptible to glare, where the phone requests dialtone at the same time that the CO sends a call.
    - Can connect two different calls if in a business with multiple lines
- Ground start signaling
  - The circuit is temporarily completed to signal the CO for services
  - Doesn’t connect any call to any phone directly
  - Used in PBXes.
- Supervisory signaling
  - On-hook: Circuit is open
  - Off-hook: Circuit is completed
  - Ringing: AC current generated by CO to tell the phone to ring
- Informational signaling
  - Gives information for the caller to use
  - Dial tone
  - Busy
  - Ringback: the ring you hear when you call
  - Confirmation: the call is being attempted
  - Congestion: no lines available to make the call
  - Receiver off-hook
  - Reorder: can’t make the call
  - No such number: can’t find the endpoint
- Address signaling
  - Used to send digits
  - Dual-tone multifrequency (DTMF): uses two electrical signals to indicate a digit; touch tone
  - Pulse: flashes the circuit to indicate a digit; rotary dial
- Disadvantages of analog signaling
  - Attenuation
  - Repeaters can’t differentiate between call and noise
  - One cable pair for each call; think about a pair for each call taking place in Manhattan right now
Digitizing voice

ROUTE Notes - OSPF Virtual Links and Frame Relay Stuff

Mon, 21 Jun 2010 00:00:00 +0000

Feel free to correct. I feel like I’m missing a big piece here, so please fill in a gap if you see one. Thanks. :)

Study Questions

How many area 0s (zero) can you have in an OSPF implementation

Just one.

If my company merges with another company, and we’re both running OSPF, how can we get our networks routing together properly?

The easiest thing to do is to connect your two area 0s together through some physical link. If you can, you can use virtual links to connect an ABR to another ABR to extend the zones together.

ISCW Down, Three To Go

Thu, 10 Dec 2009 00:00:00 +0000

I took and passed the ISCW test today. I was super-nervous going into it, which is weird for me, but I finally calmed down after the first few questions. Here’s my take. I don’t want to get into any trouble so I’m not going to include very much detail.

The testing center wasn’t very good at all. It’s in an old building on the busiest road in town, and the noise from the street was barely dampened by the 1960s building materials. I can tell you that there are three different pipes in the walls since their vibrations resonated through the room every time somebody flushed or brewed some coffee. There was also a little foot traffic, which can be expected anywhere; they were working through some software problems on another testing station and were very respectful, so it wasn’t too bad. The worst part of the whole ordeal, though, was the Microsoft class I sat through while taking the test. They were across the hall, but it sounded like they were in the room with me. Usually, you hear the instructor yelling at the top of his lungs so the whole class can hear, but I could hear questions being asked and papers being moved. I think I can go pass a test of AD replication, though. I certainly won’t be using that facility for any more tests.