Tuesday, March 18, 2014

CCNP - ENTERPRISE - DESIGN - Command Reference

This article looks to collect together the most frequent commands associated with the CCDP ARCH exam.

The point being that these are easy marks to pick up on the exam when you get a question such as 'Name the command that allows you to [insert task here]'

This list is by no means complete and I'll add further commands as I find them.

OSPF - Originate a default route in to OSPF
    #router ospf 10
        #default-information originate [always]

OSPF - On the ABR filter out all advertised routes accept those listed in the range command
Limits the size of the DB and reduces the flooding internally
    #router ospf 1
         #area 20 range

OSPF - On the ASBR filter routes sent out externally to those explicitly listed.
    #router ospf 20
         #summary address [prefix] [mask]

OSPF - Tune the OSPF hello timer interval for faster convergence
    #interface f0/0
        #ip ospf hello-interval [seconds]

OSPF - tune SPF timers to increase efficiency
    #conf t
          #timers throttle spf [spf-start] [spf-hold] [spf-max-wait]

OSPF - Increase the reference bandwidth to factor in high speed link such as 10GB ethernet, do this across all links for consistency
    #router ospf 20
          #auto-cost reference-bandwidth 10000 (for 10Gb ethernet links)

EIGRP - Originate a default route in to EIGRP
    #conf t
         #ip default-network [network ip]

EIGRP - configure unequal-cost load balancing
    #router eigrp 1
       #variance 2

BGP -configure neighbor as a Client of the route reflector
    #router bgp 65123
        #neighboor route-reflector-client

IPv6 - enable IPv6 routing for use with RIPng, EIGRP for Ipv, OSPFv3 etc
    #conf t
         #ip v6 unicast-routing

IPv6 - Define a base prefix to use for addressing:
  #conf t
       #ipv6 general-prefix [prefix]

CEF - Eliminate CEF Polarisation where one redundant link ends up being preferred to the other
    #conf t
         #mls ip cef load-sharing

EtherChannel - Use this to ensure all links within an Etherchannel bundle are utilised effectiviely
    #conf t
        #port-channel load-balance src-dst-port

FlexLinks  - Configure a port to act as a resilient backup for FlexLinks. Configure this on the primary link.
    #interface f0/10
       #switchport backup-interface [interface id]

Friday, March 7, 2014

CCNP - ENTERPRISE - DESIGN - Well Known Multicast Addresses

In the CCDP ARCH exam there are numerous refereences to Multicast addresses.

This post is to simply catalogue those that are specifically refered to in the various reading materials I've covered.

Address Scope:
  • /4 - Class D reservation
Address type:
  • to - assigned by IANA for services (detailed below)
  • to - Control Block - assigned by IANA for traffic crossing public networks e.g.- NTP
  • to - AD-HOC block assigned by IANA for addresses that don't fit the above ranges
  • to - AD-HOC block assigned by IANA for addresses that don't fit the above ranges
  • to  AD-HOC block assigned by IANA for addresses that don't fit the above ranges
  • - Source-Specfic Multicast Addresses
  • - GLOP addresses - Originally experimental now publically assigned addresses for use by ISPs and any organisation want to ublich content over Multicast
  • - Uni-cast Prefix addresses
  • - Administratively scoped IPv4 addresses, locally assigned, not globally unique
Well Known Addresses:

  • The All Hosts multicast group addresses all hosts on the same network segment.

  • The All Routers multicast group addresses all routers on the same network segment.

  • The Open Shortest Path First (OSPF) All OSPF Routers address is used to send Hello packets to all OSPF routers on a network segment.

  • The OSPF All Designated Routers ""(DR)"" address is used to send OSPF routing information to designated routers on a network segment.

  • The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment.

  • The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.

  • Protocol Independent Multicast (PIM) Version 2

  • Virtual Router Redundancy Protocol (VRRP)

  • - 21 IS-IS over IP

  • Internet Group Management Protocol (IGMP) version 3

  • Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)

  • Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode.

  • The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements.

  • The Cisco multicast router AUTO-RP-DISCOVERY address is the destination address for messages from the RP mapping agent to discover candidates.

  • H.323 Gatekeeper discovery address

  • Simple Service Discovery Protocol address

  • Tuesday, January 14, 2014

    CCNP - ENTERPRISE - DESIGN - Spark's rules for Design

    During my studies I've noticed common themes in how to approach network design.

    In general I've found that it comes down to making the best of what you've got (unless you're Google and simply commission your own hardware and build your very own private internet - coming to home near you soon...)

    Based on that I've noted the following observations during my studies:

    • Divide and Conquer! - Large flat networks are generally a bad idea, they propagate all the broadcast/multicast traffic to all hosts, make poor use of available network resourse (bandwidth, increase work on routers/firewalls etc),  are difficult to scale, increase the impact of a network event across the environment. Where possible segment it. For example:
      • OSPF - Make use of backbone routers in Area 0 and then use different areas to limit the propagation of Link State Advertisiements. In doing this you reduce the amount bandwidth used up by the OSPF process, you reduce the about of processing load on the routers within each area and the LSA's are limited to each area (reducing the content of the Routing Table). Originate the Default Route from Area 0 and where possible make use of Stub, Totally Stubby and Not-So-Stubby-Areas to reduce LSA/Route propagation.
      • Campus Design - Make good use of Hierarchical designs with a Core, Distribution/ Aggregation, Access Layers. These scale well, limits broadcast domains and make troubleshooting more logical
      • IP Address Assignment - Use contiguous networks and avoid any discontiguous subnets. Contiguous subnets makes address assignment easier (more efficient allocation of address space), troubleshooting easier, you can trace through the network easier, allows for efficient route summarisation and redistribution.
    • Summarise it! - Expanding on the previous point, when advertising routes, where possible advertise summary routes for destinations in a given area/zone. By advertising a summarised route you are reducing the size of routing tables on upstream routers and you then limit the impact of route flaps within the network. If a single link goes down then a route that is advertised as a /30 would need removing from all routers that have a route for this network. If the failed link falls under a /24 route then the upstream routers don't observe the link flap and do not have to re-calculate the shortest path which inturn means that resources on upstream routers are not utlised unneccesarily.
    • Keep It Simple! - At the dead of night that on call network engineer will not thank you for building that convoluted network that makes use of lesser know commands just because it's fancy. Always consider how difficult troubleshooting the proposed solution will be and keep it simple. For example:
      • Avoid OSPF virtual links - an network outage in the transit area could cut off the remote area to area 0
      • Keep access lists consistent - Agree on a naming convention for access lists, object-groups, hosts. Agree on how an access list will be named and how it will be constructed and stick to it. Being consistent will make for a cleaner running-config and will make reading it easier which in turn should make troubleshooting easier
    Now, the point of the rules above is to apply each rule as measure of how to approach exam questions. For any given question can the rules above be applied and the correct answer revealed? (Of course you should know your stuff when it comes to sitting an exam but sometimes you get blind sided by a badly worded question)

    Remember to be methodical and ultimately consider What Would Cisco Do...?