>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
What I meant to say is that the full document is on
CertificationZone, but, as an older White Paper, is in the
subscriber-only area. Part A dealt with non-default route selection.
>
>
>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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>
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