Unfortunately there is no easy way to recover a corrupt or deleted IOS image on a fixed configuration Cisco Catalyst switch. You must use xModem which commonly takes 2+ hours. This lab will discuss and demonstrate the IOS recovery procedure for fixed configuration Catalyst series switches using xModem.
Recovering the Cisco IOS image on a Cisco switch is one of those tasks that is nice to know and not need it then need it and not know it. In the field you may find yourself faced with a Cisco switch that cannot boot up or crashes when booting up due to a possible IOS Image corruption.
بکارگیری پروتکل RIP در شبکه های کامپیوتری بیشتر به دلیل شرایط زمان بوده است. در ده هفتاد و هشتاد حافظه و پردازندههای سریع ، گران قیمت بودند و پیاده سازی الگوریتمهای مسیریابی مبتنی بر روشهایی نظیر LS که هم به حافظه و هم به پردازندۀ سریع نیاز دارند ، مقرون به صرفه نبود. از طرفی شبکه ها نیز آنقدر توسعه نیافته بودند که نیاز به الگوریتم های بهینه تر احساس شود. با گسترش اینترنت و توسعۀ شبکه های خودمختار در اواخر دهۀ هشتاد ، کاستی های پروتکل RIP نمود بیشتری پیدا کرد و با سریع شدن پردازنده ها و ارزان شدن سخت افزار ، نیاز به طراحی یک پروتکل بهینه ،IETF را واداشت تا در سال 1990،OSPF را به عنوان یک پروتکل استاندارد ارائه نماید. مسیریابهای زیادی مبتنی بر این پروتکل به بازار عرضه شده اند و احتمال می رود که در آینده تبدیل به مهمترین پروتکل مسیریابی درونی در شبکه های AS شود.
R1 has an EBGP peer to R5 and an IBGP peer to R2.
R2 has an EBGP peer to R4 and IBGP peer to R1.
Ensure that the 15 loopbacks on R1 (188.8.131.52–184.108.40.206/24) are advertised to R5 and that R5 modifies all even networks with a local weight to 1000 and metric (MED) to 100. For all odd networks, set the weight to 2000 and the metric (MED) to 200.
Ensure that R1 advertises a default route to R5 and that R2 advertises a default route to R4. Use a prefix list to accomplish this task.
Ensure that R4 does not accept any networks in the range 220.127.116.11 but does accept a default route only. All other networks must be denied on R4.
Ensure that R3 can reach all BGP-advertised networks using OSPF as the only routing protocol. (That is, redistribution is required on R1/R2).
In this scenario, you build upon the IBGP network and configure EBGP on R1 and R2 and simulate a dual-homing ISP connection. Because most CCNP candidates do not have two ISP connections to configure in a lab environment, you configure two routers and inject default routes along with a large IP routing table to simulate an ISP router.
Configure the routers ISP1 and ISP2 for EBGP and advertise a default route to the internal BGP network along with some routes that simulate an Internet environment.configures ISP1(R6) for EBGP and allows a default route to be advertised to the EBGP peer to R1.
سناریویی آماده کردم در مورد BGP Route Reflector .
Consider a network consisting of 100 routers. Having this many routers leads to alarge number of TCP BGP peers. In fact, you can easily calculate the number of peers by using the formula n(n-1)/2, where n is the number of BGP routers.
To avoid routing loops, BGP only propagates updates learned from IBGP connections to other IBGP sessions that are fully meshed. Fully meshed networks contain a BGP peer to every BGP speaker in the network. For a 100-router network, there are 100(100-1)/2 = 100(99)/2 = 4950 TCP peers.
IBGP works well in small networks, and as the network grows even to just 100 routers, the scalability and administration of BGP becomes a task you must carefully consider.
BGP deals with large BGP networks using two methods:
· Route reflectors
· Confederations (advanced form of route reflectors; confederations are beyond the scope of this chapter.)
شرح ، توضیحات و پیکربندی به شرح زیر میباشد.
the Routers R1–R5 are part of a large company and route reflectors are configured on R1 and R2 for redundancy purposes.Enable OSPF on the IGP routers by enabling all interfaces in area 0, so you can take advantage of loopbacks for the source and destination address for all IBGP peer sessions.
onfigure IBGP on R1 and use the loopback addresses as the next hop addresses because as long as you have IP connectivity, BGP should remain active. In
fact, good IBGP design always uses loopbacks so that one routing failure does not result in loss (TCP fails) of IBGP connectivity.
lo 0 for all routers : 131.108.254.x (x is number of each routers)
ospf configs on all router : R1-R5:
R1(config)#router ospf 1
R1(config-router)# network 0.0.0.0 255.255.255.255 area 0
The reason that OSPF is chosen for the preferred path is that OSPF has a lower nadministrative distance of 110, compared to 200 for IBGP.
if EBGP is configured between two routers and OSPF is the interior routing protocol, EBGP administrative distance is 20, far lower than OSPF (AD is 110). By default, a lower AD is always preferred; therefore, the next hop address is the EBGP
To change this default behavior without the changing AD values, use the network <network subnet-mask> backdoor command. Specifying the network allows the router to choose OSPF as the preferred path rather than the EBGP discovered path.
Changing the administrative distance is not always the most desirable method because all routers typically need modification, as in this scenario.
R1 is configured for EBGP and IBGP. The EBGP connection to the remote peer address, 18.104.22.168, is the Internet gateway. Therefore, you must send the
community to the remote peer and apply an outbound route map, so the Internetrouters do not use R1 as a transit path. You have yet to apply the route map named setcommunity (arbitrary name). Apply the well-known community no-export, which informs the neighboring router not to use R1 for any traffic not destined for the network 22.214.171.124/16.
configure the four routers, R1–R4, for IBGP, and set the same policies on all four routers.
ensure that R1 does not receive any default routes from R2, R3, or R4 (sets the next-hop-self attribut. Ensure that R1 sets the community to the value 2000.