Well, I've been playing with a cisco rack. Actually I managed to get 4 serial links up (isn't it great?
Clarifying the Cisco IOS bandwidth command. The EIGRP metric are bandwidth and delay. You configure the Cisco IOS. Of a serial interface, the default bandwidth is 1,544 K (or a. If a bandwidth is not configured on a subinterface, and you use the bandwidth inherit command, all subinterfaces will inherit the current bandwidth of the main interface. If you configure a new bandwidth on the main interface, all subinterfaces will use this new value.
LOL!) but I realized that I don't have clear the difference between: 1.- clock rate 2.- Bandwidth According to my study book, clock rate is used when the router has to provide signaling (ie be a DCE). Now, is this clock rate related to the serial line speed?
IE: a T1 (1.544 Mbps), how would you configure it on the serial int? Bandwidth, on the other hand, is used for routing protocols. Is this correct? I ended up using clock rate 64000 and bandwidth 64 without knowing why exactly.
And I don't like that! Can someone show the light? Saludos amigos!
Interface Configuration Configuring interfaces involves more than simply plugging in the cable andactivating the interface with the IOS Software command no shutdown.Attention should be applied to details such as whether it is a WAN or a LAN,whether a routing protocol is running across the interface, addressing and masksto be used, and operator information. Description Use the description interface command to document details such asthe circuit bandwidth, the customer name, the database entry mnemonic, thecircuit number that the circuit supplier gave you, and the cable number. Thissounds like overkill, especially if there is a customer database within the ISPorganization. However, it is very easy to pick up all the relevant details fromthe router show interface command if and when an engineer needs to be onsite,when an engineer is away from the database system, or when the database isunavailable. There can never be too little documentation, and documentation suchas this ensures that reconstructing configurations and diagnosingproblems are made considerably easier.
Bandwidth Don't forget the bandwidth interface command. It is used byinterior routing protocols to decide optimum routing, and it is especiallyimportant to set this command properly in the case of backbone links using onlya portion of the available bandwidth support by the interface. For example, aserial interface (Serial0/0) on a router supports speeds up to 4 Mbps but has adefault bandwidth setting of 1.5 Mbps. If the backbone has different size linksfrom 64 Kbps to 4 Mbps and the bandwidth command is not used, theinterior routing protocol will assume that all the links have the same cost andwill calculate optimum paths accordinglyand this could be less thanideal. On customer links, it might seem that this setting is superfluous because aninterior routing protocol is never run over a link to a customer.
However, itprovides very useful online documentation for what the circuit bandwidth is.Furthermore, the bandwidth on the circuit is used to calculate the interfaceload variablesome ISPs monitor their customer interfaces loading by SNMPpolls so that they can get advance warning of problems or congestion, or toproactively inform customers of necessary upgrades. (Some ISPs look at the loadvariable; other ISPs look at the five-minute average, inbound and outbound. Ifyou monitor the load variable, you need to set the bandwidth so that it matchesthe true circuit bandwidth, not the default configured on the router.) ip unnumbered Traditionally ISPs have used IP addresses for the point-to-point links onleased-line circuits to customers. Indeed, several years ago, before the adventof CIDR, it was not uncommon to see a /26 or even a /24 used for simplepoint-to-point link addresses.
With the advent of CIDR, /30 networks have beenused instead (/30 is a block of four addresses, two of which can be used forphysical interfaces). However, this led to problems because IGPs of some of thelarger ISPs were starting to carry several thousand networks, affectingconvergence time and resulting in an administrative and documentation nightmare. To avoid problems with large numbers of /30s floating around the ISP'sinternal routing protocol, and to avoid the problems of keeping internaldocumentation consistent with network deployment (especially true in largerISPs), many are now using unnumbered point-to-point links. An unnumbered point-to-point link is one requiring no IP addresses.The configuration is such that traffic destined for one network from anothersimply is pointed at the serial interface concerned.
Ip unnumbered isan essential feature applicable to point-to-point interfaces such as Serial,HSSI, POS, and so on. It enables the use of a fixed link (usually from ISP tocustomer) without consuming the usual /30 of address space, thereby keeping thenumber of networks routed by the IGP low. The ip unnumbered directivespecifies that the point-to-point link should use an address of anotherinterface on the router, typically a LAN or more usually a loopback interface.Any networks that must be routed to the customer are pointed at the serialinterface rather than the remote address of the point-to-point link, as would bedone in normal instances.
Caveats ISPs need to consider some situations before implementing an IP unnumberedsystem for their customer point-to-point connections. These are considerationsonlybear in mind that many ISPs have used IP unnumbered for several years,mainly so that they can control the size of the IGP running in their backbonenetwork. Pinging the customerMany ISPs use monitoring systemsthat use ping to check the status of the leased line (customerconnectivity). Even if the customer unplugs the LAN, an alarm will not be raisedon the ISPs management system. This is because the customer router still knowsthat the LAN IP address is configured on the system and is 'useable.'
As long as the IP address is configured on the LAN, there will be noreachability issues with using ip unnumbered. Routing protocolsIf a routing protocol needs to be run over thislink, it is operationally much easier to use IP addresses.
Don'tuse ip unnumbered if the customer is peering with you using BGPacross the link or if the link is an internal backbone link. Simply use anetwork with a /30 address mask.
(Routing will work over unnumbered links, butthe extra management and operational complexity probably outweighs the smalladdress space advantage gained.). Loopback interfaces on the customer's routerTheseoffer no advantage to addressing the ping problem, and theyunnecessarily consume address space (not to mention adding complexity to thecustomer router configuration).