Cisco Hands On Training Podcast - IOS Version Selection Tactics

IOS Version Selection Tactics

03/14/10 • -1 min

The linked video provides guidance for optimal IOS version selection.

The large number of IOS versions makes choosing the best version for your router or switch difficult. You must pick the most reliable version which includes the features you need. Different IOS "packages" have different features. For example, the "LAN base" package includes basic switching code. "IP base" adds access-layer routing features (RIP and EIGRP-stub). "IP services" adds most layer-3 routing protocols (OSPF, EIGRP, BGP). "Advanced IP services" adds IS-IS and MPLS.

Picking a version also means picking one with recently introduced features you need. For example, 16-port 10-gigabit ethernet card support was added to the 6500 line in 12.2(33)SXH code. If you require that card, you cannot pick an older version, such as 12.2(18)SXF. The release notes include details on recently added features.

Finally, of all the versions that have the features you require, you want to pick the most stable version. That means picking a version that has been "rebuilt" with many bugfix-only releases. Picking 12.4(2)T, where 60 new features were just introduced, would be a bad idea. On the other hand, 12.4(23) (the lack of a letter means it is a mainline release) would be a good choice because that release has undergone dozens of releases since significant numbers of features were introduced.

The linked video provides guidance for optimal IOS version selection.

Previous Episode

IOS Access Control Lists

In this video demonstration, we show an example of writing IOS Access Control Lists (ACL's) on a home router. We use the revision control system (RCS) to maintain the master ACL file and push the ACL's to the router via TFTP. This is similar to many production networks, where maintaing comments and old revisions of ACL's is a requirement. We also show examples explaining the "don't care bit" format of IOS ACLs. Many network engineers mistakenly refer to the format as inverse-netmask, but that is incorrect.

PIXes, FWSMs, and ASA's use a netmask format for ACLs. It is vitally important not to make the mistake of accidentally pushing a netmask format ACL line to an IOS device. That sort of error could result in an unplanned hole in your firewall and a serious security incident.

Next Episode

IPv6 theory

The linked video introduces IPv6 theory. IPv6 is the 128-bit address replacement for IPv4. The Internet is expected to run out of it's 4-billion IPv4 addresses in 2012. IPv6 will replace IPv4 at the network-layer of the OSI stack. By replacing one layer in the stack, most applications and most layer-2 network devices will continue to function.

IPv6 includes several technical improvements over IPv4. IPv6 uses optional extension headers, so only packets requiring special options will have those headers. As a result most IPv6 packets will have simpler headers than their IPv4 counterparts. IPv6 eliminates broadcast, and instead uses multicast for most neighbor discovery functions. This is more efficient CPU-wise because hosts only need to subscribe to the multicast groups they require. IPv6 hosts use stateless autoconfiguration to acquire link-local and internet routable IPv6 addresses. In many cases this can eliminate the need for a separate DHCP server. And of course IPv6 includes 128-bit addresses, allowing 256 billion billion billion billion hosts.

The migration from IPv4 to IPv6 will be the highlight and most significant change of our networking careers. Most of us were not in this business during the IPv3 to IPv4 migration on January 1st 1983 (a 'flag day' migration). Odds are IPv6 will remain the dominant internet protocol until after we retire.

A PDF version of my presentation will be attached to the comments section.