Hi, Howard.
I just want to know what you mean by "subscribers only".
Does that mean you're running your own mailing list or something like
that? It seems to me it's just portion of what you've published on
that list before. Or from CertificationZone, maybe.
Well, I'm just curious about what missing "A" will be like.
Thanks
Regards,
Jaeheon
On 28 Jan 2001 20:57:10 -0500, [EMAIL PROTECTED] ("Howard C. Berkowitz")
wrote:
>subscribers only), Routing Principles and IOS Implementation
>Considerations:
>
>B. Default Whatevers
>You will run across several terms that are often, and incorrectly,
>considered synonymous: default routes, default gateways (default
>routers), default networks, and gateways of last resort. These terms
>refer to slightly different mechanisms, all of which are useful. This
>section explains what each mechanism does.
>
>1. Default Route
>
>By convention, the address 0.0.0.0/0 is the default route, the least
>specific possible route. Cisco sometimes uses the term pseudonetwork
>to refer to 0.0.0.0/0. It is the route that you go to when you don't
>have anyplace else to go. When it came time to pick softball teams in
>my high school physical education classes, I was the default route.
>
>As opposed to being something to put in right field and forget,
>default routes are quite useful in networking. They can be declared
>with static routes, or they can be learned from dynamic routing
>protocols. To create a static route defining the local default, code:
>
> ip route 0.0.0.0 0.0.0.0 {next hop IP | outgoing interface}
>
>Created as a static route with an administrative distance less than
>dynamic routing, a default route in the next-hop-ip format will be
>used for the local router box, but not advertised unless it is
>explicitly redistributed (or you use the outgoing interface form of
>the static route command).
>Statically declared default routes of the interface-name format will
>be advertised as if they were directly connected.
>
>Local configuration is not the only way your router can learn the
>0.0.0.0/0 default route. It can be learned from dynamic routing
>protocols such as OSPF and RIP. In the more recent IOS releases, you
>can originate default from any of these routing processes with the
>default-information-originate command. When you do this, the process
>will advertise default to other routers, although it might use,
>itself, the static route.
>default-information-originate has an optional parameter, the always
>keyword. If you don't use always, the router will advertise default
>only if it itself has an active default route.
>
>With always, the router will always advertise default, and will have
>the behavior that it will blackhole routes to unknown destinations if
>there is no default. A typical application for always would be where
>you have a single ISP link to which you default, so you might as well
>blackhole if you can't get to it.
>
>2. Default Gateway
>
>The default gateway is specifically intended for the situation when
>no IP routing is enabled. It has the specific next hop address of the
>gateway router.
>
>You would use this on a switch, or a router box that is only doing
>bridging, so the box can reach network management servers not on the
>same subnet. Another application for the default gateway comes during
>booting from ROM, to find the TFTP server.
>
>In the IOS, you configure an IP default gateway with the command:
>
>ip default-gateway gateway-address
>
>where gateway-address is the address of a router interface on a
>subnet to which your router is physically connected.
>
>3. Default Network
>
>The default network, used by IGRP and EIGRP, has only a prefix -- a
>network or subnet -- so unless internal assumptions are made, there's
>no way to know the specific next hop address.
>
>Always remember the KISS (Keep it simple, stupid) rule. Once you
>understand what command is intended to do something, it isn't always
>useful to keep looking for commands that might do the same thing. The
>major reason to look for obscure command interpretations is that they
>may be the cause of problems you are troubleshooting.
>
>In the real world of network design, the KISS rule is critical. On
>the CCIE test, however, be prepared to be faced with scenarios that
>violate this rule. One of the drivers of CCIE scenario writers seems
>to be that you are very familiar with obscure parts of the IOS
>command language. In addition, some CCIE lab scenarios may seem quite
>contrived, due to the relatively small number of available routers.
>
>For those of you who have taken ACRC, you have had an experience that
>will give you perspective on odd scenarios you may see. ACRC's
>redistribution and BGP scenarios are very unrealistic with respect to
>plausible real-world configurations. They are the best that can be
>done with the standard classroom lab and its topology.
>
>See Scenario 2 for examples of the various default mechanisms.
>
>To specify a default network for IGRP or EIGRP, or that will be known
>locally on your router, code:
>
>ip default-network ip-prefix
>
>The ip-prefix is not a host address as used in the next hop field of
>an ip route statement, or as the argument of a ip default-gateway. It
>is a network or subnet address (i.e., with all zeroes in the host bit
>positions).
>
>4. Gateway of Last Resort
>The gateway of last resort (GOLR) is selected by the process that
>actually installs routes in the routing table. The GOLR represents
>the default destination that comes from the source of default that
>has the lowest administrative distance (AD).
>
>So if you had a default static route, it would become the GOLR
>regardless of anything you received from any routing protocol. If you
>received a default network from EIGRP or IGRP, that network would
>become GOLR in preference to anything from RIP or OSPF, unless you
>changed the administrative distance for RIP or OSPF. An OSPF default
>would be preferred to anything from RIP. An OSPF Type 1 default would
>be preferred over an OSPF type 2 default.
>
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