Ccie on Aaron's Worthless Words

CCIE R&S Written -- Epic Fail (Again Again)

Wed, 07 Aug 2013 00:00:00 +0000

On Friday, and for the fourth time, I took the CCIE R&S Written exam (350-001). For the third time, though, I failed. Let me tell you, I am absolutely devastated. I worked my buns off for the past few weeks, but I’m obviously missing some important piece to put me over the top.

Not only was I disappointed with my overall score, I was disappointed by my score in some of the focus areas. For God’s sake, I made a 50% on each of the routing and switching sections, which is just absolutely embarrassing. I mean, this is my bread and butter here. This is what I do all day every day, and I could only muster a 50%?

QoS Notes - IPP and DSCP Values

Tue, 30 Jul 2013 00:00:00 +0000

This is a study note post, so please don’t take this as written. I’m not the authority on the subject, so please correct me if needed.

Back in the day, somebody decided that we all needed to have a Type of Service (ToS) field in the header of IP packets. Only God knows what this spawn of Satan wanted to do with it, but we’re stuck with it on the CCIE R&S exams.

CCIE R&S Written - Epic Fail (Again)

Sun, 07 Jul 2013 00:00:00 +0000

Yes, I failed. I think it’s pretty typical when you’re at Cisco Live, you stay out drinking and smoking cigars until 01:00, then you sit the exam at 08:00 the next morning. Considering the situation I put myself in, I wasn’t very optimistic about passing, but I figured I had maybe a 40% chance to pass since I didn’t really even study. Are you sensing a theme of ill-preparedness and self-sabotage? Yeah, me, too.

CCIE R&S Written - Epic WIN!

Wed, 24 Aug 2011 00:00:00 +0000

The wife and I had a romantic day driving several hours to a small town to take Cisco exams. If this doesn’t get me some action, I don’t know what else to try.

I’ve already used the phrases “skin of my teeth” and “a pass is a pass” on Twitter today for good reason. Passing is a score of 790, and I blew that away with a 790. One more lapse in concentration and I would have been making up more excuses instead of smiling. I think I’ve mentioned this before, but I have this weird reaction to taking exams where I don’t get nervous at all until after I’m finished. Walking into the testing center, I was fine. Walking out, I was shaking like Northern Virginia. It was so bad that I could barely hold on to the door knob when trying to leave, so I guess that I’m really prouder than I thought I was.

OSPF and Loopback Interfaces

Sun, 31 Jul 2011 00:00:00 +0000

I was studying via Google+ Hangout the other day with CJ and Rob, and one of the topics that came up was that OSPFv2 advertises all loopbacks as 32-bit no matter what the configured mask is. I rarely use loopbacks outside of a lab and had no idea it did that, so I set up a quick lab to see for myself. Sure enough! That’s exactly what I saw.

Of course, being the inquisitive network guys that we are, we went on to discuss methods for making OSPF advertise the configured network instead of the single IP. The guys mentioned two methods - to redistribute the connected interfaces and to manually set the OSPF network type on the loopback. We were using IPv4 during the session, but I went back and added some IPv6 addresses and processes to compare.

CCIE R&S Written - Epic Fail

Tue, 19 Jul 2011 00:00:00 +0000

It’s been a long time, eh? I’ve spent the last month or so with my nose down in a book and my mouse in a Google+ Hangout window studying my rear off for the CCIE R&S Written. Too bad I didn’t pass it.

The exam consisted of 77 questions over a 2 hour window. That’s plenty of time to finish; I think I had 48 minutes left when I was through, so time wasn’t a problem. There were only 2 or 3 questions where I was totally lost, so the technology wasn’t a problem. The big problem, like always, was the usual crap questions that are in these exams. Some didn’t provide all the required information. Some were impractical examples of deployments you would never use in the field. Some were on deprecated technologies. Hell, I had one that involved CatOS. Really? CatOS? Since I only failed by about 2 questions (like I always do), these shenanigans are magnified in my mind. It really irks me how these exams are being done; foggy questions don’t really measure ability.

Frame Relay Notes - DE, FECN, and BECN

Thu, 23 Jun 2011 00:00:00 +0000

All are part of the frame relay congestion management suite.
Frame relay switches monitor links for CIR or oversubscription congestion on links.
- If the VC has a CIR of 256k, the switch knows there is congestion if the customer is sending more than 256k down that VC.
Discard Eligible
- Flag in the LAPF header
  - Marks a frame as eligible to be dropped in case of congestion
  - Marked via the MQC
Forward Explicit Congestion Notification
- Flag in the LAPF header
- Set by the switch when the frame is about to enter a link with congestion on a VC
  - Congestion in one direction
  - FECNs are set when the frame is going into the congestion.
- Receiving router can see that there was congestion on the way.
- FECNs can be used to activate adaptive shaping via FRTS.
- Plain English: If Router B receives a frame with the FECN flag set, that means that there is congestion on the path from Router A to this Router B, and that Router B should expect delays.
Backward Explicit Congestion Notification
- Flag in the LAPF header
- Set by the switch when a frame has just left the link with congestion
  - Congestion is the opposite direction.
  - BECNs are set when the frame has just left a link that has congestion on it.
- Notifies the original sending router that there is congestion along that VC.
- Plain English: If Router A receives a frame with the BECN flag set, that means that there is congestion from Router A towards Router B and that the sending host should calm down a little bit.

http://www.sinclair.org.au/keith/networking/frame_relay.html – Corrections requested.

Frame Relay Notes - LMI, Headers, and Encapsulation

Thu, 23 Jun 2011 00:00:00 +0000

Local Management Interface

Manages link between the router and frame relay switch
Routers send Status Enquiry to the switch
The switch responds with a Status message informing the router of the DLCIs available
Serves as a keepalive
Default keepalive is 10 seconds, 3 misses is failed
Three types
- cisco <- default
- ansi (Annex D)
- q933a

R1(config)#interface s1/0
R1(config-if)#frame-relay lmi-type ansi

Headers and Encapsulation

Link Access Procedure for Frame-mode Bearer Services (LAPF) is the first header
- Includes DLCI, DE, FECN, BECN
- To be read by the frame relay switch
Frame relay encapsulation header is next
- To be read by the router on the other end of the VC
Two types
- cisco : proprietary <- default
- ietf : IETF RFC 2427

R1(config)#interface s1/0
R1(config-if)#frame-relay encapsulation ietf <- for all DLCIs
- or -
R1(config-if)#frame-relay interface-dlci 100 ietf <- for specific DLCIs
- or - 
R1(config-if)#frame-relay map ip 10.0.0.1 ietf <- for specific DLCis

PPP Notes - LFI

Thu, 23 Jun 2011 00:00:00 +0000

Link Fragmentation and Interleaving
A QoS tool to prevent smaller, higher-priority packets from waiting on larger packets to transmit
- For example, VoIP packets and FTP packets
Fragments the larger packets and interleaves them with the smaller packets
Only available in PPP with Multilink
- Can be a multilink bundle with a single link in it
Common to use with LLQ to interleave the delay-sensitive packets
fragment-delay allows you to change the fragment size
- In milliseconds
- size = fragment-delay * bandwidth of interface

R1(config)#interface Multilink 1
R1(config-if)#bandwidth 512
R1(config-if)#ppp multilink interleave
R1(config-if)#ppp multilink delay 10

-- Corrections, please.

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

CCIE R&S Written Materials

Mon, 13 Jun 2011 00:00:00 +0000

I’m scheduled to take the CCIE R&S Written exam on 10 July at Cisco Live, and I’ve been asked by a handful of people on Twitter exactly what materials I’m using. I figured it would be a good idea to let everyone know so that we all can determine whether or not I’m on the right track. I may get to the exam and find out that the books I’ve been reading aren’t even close. It’s happened before.

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

Comment with corrections, please

BGP Notes - Confederations

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

RFC 3065
BGP confederations reduce the size of full mesh iBGP ASes by dividing it up into different areas.
Confederations also remove the need for BGP synchronization since all iBGP routers will have all routes.
In effect, your iBGP AS gets chopped up into different sub-ASes.
Each router is a member of a sub-AS and is a neighbor with every other router in that sub-AS (full mesh).
- Neighbors within a sub-AS are called confederation iBGP neighbors.
- Confederation iBGP neighbors act just like any other iBGP neighbor.
At least one member of each sub-AS is neighbored with members of different sub-ASes.
- Neighbors in different sub-ASes are called confederation eBGP neighbors.
- Confederation eBGP neighbors have a default TTL of 1 just like true eBGP neighbors.
- The NEXT_HOP PA is not changed when passing routes between sub-ASes.
- LOCAL_PREF is also preserved.
Confederations use the AS_CONFED_SEQ and AS_CONFED_SET fields in the AS_PATH PA.
- These fields act like AS_PATHs to prevent loops.
- These fields are cleared out when the route is passed to an eBGP neighbor.
- If components of a summary route (an aggregate-address) have different AS_CONFED_SEQ values, the AS_CONFED_SET is used.
Confederations ASes are not included when the router decides which route is best.
BGP confederation routers are configured to be in a private ASN.
- The confederations should be private to avoid AS conflicts.
- The confederation identifier defines the AS at it appears to the world.

router bgp 65001
 no synchronization
 bgp confederation identifier 123
 bgp confederation peers 65002 65003
 neighbor 2.2.2.2 remote-as 65002
 neighbor 3.3.3.3 remote-as 65003

Comment with corrections, please.

BGP Notes - Route Reflectors

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

Route reflectors remove the requirement of having a full mesh iBGP network.
Any iBGP route a router reflector learns is sent to all route reflector clients.
- Non-client iBGP neighbors do not get the new route per iBGP rules.
RR clients are configured like normal iBGP routers.
- All RR client config is done on the route reflector.
RRs and clients are part of a cluster.
- RRs in each cluster must be neighbors with each other.
- Each cluster RR appends the cluster ID to the CLUSTER_ID PA; this is used similarly to AS_CONFED_SEQ.
The ORIGINATOR_ID PA is set by and preserved by the RR.
- If a route contains the ORIGINATOR_ID of the receiving router, the update is ignored.
Only best routes are passed to RR clients and non-client neighbors.

router bgp 123
 no synchronization
 bgp cluster-id 1
 neighbor 6.6.6.6 remote-as 123
 neighbor 6.6.6.6 route-reflector-client

Comment with corrections, please.

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.

These are just some notes I’ve been taking. Comment with corrections, please.

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

EIGRP Notes - Authentication

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

Corrections - I invite them.

1. Create the keys in the keychain.

R101(config)#key chain KEYCHAIN
R101(config-keychain)#key 1
R101(config-keychain-key)#key-str
R101(config-keychain-key)#key-string MYKEY

2. Enable authentication on an interface.

R101(config-if)#ip authentication mode eigrp 1 md5

3. Associate keychain with EIGRP.

ip authentication key-chain eigrp 1 KEYCHAIN

OSPF Notes - Authentication

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

Corrections appreciated.

Type 0 : No authentication. This is the default type.

R0(config-if)#ip ospf authentication null
-----
R0(config-router)#area 1 virtual-link 2.2.2.2 authentication null

Type 1 : Clear text authentication

-----
R0(config-if)#ip ospf authentication
  - or -
R0(config-router)#area 1 authentication
R0(config-if)#ip ospf authentication-key MYKEY live sex online
-----
R0(config-router)#area 1 virtual-link 2.2.2.2 authentication-key MYKEY

Type 2 : MD5 authentication

-----
R0(config-if)#ip ospf authentication message-digest
  - or -
R0(config-router)#area 1 authentication message-digest
R0(config-if)#ip ospf message-digest-key 1 md5 MYKEY
-----
R0(config-router)#area 1 virtual-link 2.2.2.2 authentication message-digest message-digest-key 1 md5 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.

OSPF Notes - Network Types

Sat, 04 Jun 2011 00:00:00 +0000

Corrections are always welcome.

Broadcast : Think an Ethernet segement

DR/BDR? : Yes Default hello interval : 10 sec Neighbor config required? : No

Point-to-point : Physical point-to-point links, frame-relay point-to-point subifs

DR/BDR? : No Default hello interval : 10 sec Neighbor config required? : No

Nonbroadcast Multiaccess : Frame-relay multipoint or physical

DR/BDR? : Yes Default hello interval : 30 sec Neighbor config required? : Yes

Point-to-multipoint : Partial mesh networks like a frame-relay hub-and-spoke configuration

OSPF Notes - LSA Types

Thu, 02 Jun 2011 00:00:00 +0000

Yes, it is inevitable that I cover these. I’m sure network types will be next. Per my usual request, please correct my stupidity.

Type 1 - Router : This LSA type lists all the routers by RID as well as the networks to which that router connects.

Type 2 - Network : These LSAs represent broadcast network where more than one OSPF router may live. Think Ethernet or multipoint segment. These LSAs are flooded by the DR for that segment.

OSPF Notes - Neighbor States

Thu, 02 Jun 2011 00:00:00 +0000

My prediction about covering network types was wrong. I’m going to puke out some information about neighbor states for now. As is always the case, corrections are welcome.

Down : No hellos have been received from this router.

Attempt : This state only applies to manually-configured neighbors on an NBMA network. In this state, a router has sent unicast hellos to the neighbor but has not received any back from it.

OSPF Notes - Message Types

Wed, 01 Jun 2011 00:00:00 +0000

I have had my nose deep in several books in preparation for my CCIE R&S written exam, so I haven’t been blogging much at all. Now that I’ve made it to the more familiar topics, I’m hoping to get some notes posted. I’ll start with OSPF message types.

As always, please feel free to correct me here. I’m learning just like the rest of us.

Hello : These messages are used to establish neighbors and serve as keepalives among other things.