Ccnp Route Notes 136260

CCNP ROUTE Notes The default-information originate always does not produce a static route in the routing table of the local router on which it is configured but it will generate a default route and it into the ospf domain OSPF FILTERING  On the ASBR o Use route-map  On the ABR o Area < > filter-list prefix < prefix-list name> [in | out]  On any router o Distribute-list < > in [This command will only prevent the filtered route from entering the routing table but the route will still appear in the ospf database] EIGRP considers the load (k2) of an interface only when sending an update for some other reason. The load is a five- minute exponentially weighted average that is updated every five seconds The neighbor command is used in EIGRP to define a neighboring router with which to exchange routing information. EIGRP stops processing multicast packets that come inbound on that interface. It also stop sending multi casts to that interface. No dynamic neighbor can be either discovered or continue to work if already discovered [over a network with more than two routers in the same subnet running EIGRP]. EIGRP exchanges routing information with that neighbor via unicasts whenever this command is used. One difference between DHv4 and stateful DHv6 is that IPv4 hosts send IP broadcasts to find DH servers, whereas IPv6 hosts send IPv6 multicasts. IPv6 multicast addresses have a prefix of FF00::/8, meaning that if the first 8 bits of an address are binary 11111111, or FF in hex. When using link local addresses as the next hop address when configuring IPv6 static routes, the outgoing interface has to be specified in the configuration. Reliable EIGRP packet types  Update  Query  Reply Unreliable EIGRP packet types  Ack  Hello OSPF Frame Relay Interfaces 1) Physical - Non Broadcast 2) Multipoint subinterfaces - Non Broadcast 3) Point to Point subinterfaces - Point to Point Show ip route ospf | begin IA show ip ospf database | begin Summary Show ip ospf database | include 172.16.4 The maximum number of LSAs learned from other routers can be limited by a router using the max-lsa number OSPF subcommand. When configured, if the router learns more than the configured number of

LSAs from other routers (ignoring those created by the router itself), the router reacts. The first reaction is to issue log messages. The router ignores the event for a time period, after which the router repeats the warning message. This ignore-and-wait strategy can proceed through several iterations, ending when the router closes all neighborships, discards its LSDB, and then starts adding neighbors again. (The ignore time, and the number of times to ignore the event, can be configured with the max-lsa command.) If no DR is required: When sending the first DD message, transition to an Exstart state. The Master/Slave relationship is established in the Exstart state. Then the neighbor is transitioned to the Exchange state The Master is the router with the highest RID Sequence Number begins with 0x80000001 and increments by 1 whenever the LSA changes RouterA#debug ip ospf events OSPF events debugging is on RouterA# 04:43:16: OSPF: Rcv hello from 172.16.1.1 area 0 from Serial0/0 10.1.1.1 04:43:16: OSPF: Mismatched hello parameters from 10.1.1.1 04:43:16: OSPF: Dead R 120 C 10, Hello R 30 C 30 The Dead R is the Dead Timer of the neighbor that in this case is 120 seconds, and the Dead C is the local Dead Timer. When pinging a link local IPv6 address, the outgoing interface will have to be specified because these addresses are are not routed and are not in the routing table. Also note that the full interface name must be specified without spaces. With Cisco Express Forwarding (CEF), layer 3 switching is done in hardware (in an ASIC) instead of by software and the central U. It is off by default on all Cisco routers To match a default route with a: 1) Standard ACL, use "access-list x permit 0.0.0.0” 2) Extended ACL, use "access-list y permit ip host 0.0.0.0 host 0.0.0.0” 3) prefix-list, use "ip prefix-list z permit 0.0.0.0/0” When redistributing IGRP into EIGRP, if they have the same ASN, they redistribute automatically else redistribution needs to be manually configured The redistribute command also tells the router to redistribute connected routes on interfaces enabled with that routing protocol including ive interfaces

Tool command language (tcl) syntax for ping & traceroute Tclsh Foreach address { A.A.A.A $ . . . $ } { ping | trace $address} To quit tcl, use the tclquit command. It takes you straight to privilege mode "Bit bucket" - A term used when a router discards a route that matches the null0 interface of a summary route N/B: for default frame relay networks, Neighbor commands configured on spoke routers will not appear in the running config if the router's OSPF priority has been set to 0 on the interface which would be used to communicate with the designated neighbor. Although you can use the "ip ospf dead-interval minimal hello-multiplier" command on serial links, it would create additional overhead on these slow links and could result in flapping adjacencies if the link begins to experience congestion. Using this command on high-speed serial links would be less of an issue When a router receives an unknown OSPF LSA, it will first of all flood the LSA out all interfaces except the interface it learned that LSA from. This is done before it sends an ACK to the transmitting router of that LSA The metric of an OSPFv3 summary route will be the worst (highest) metric of its subordinate routes Question: what technique should be used on BGP edge routers to prevent a multi- homed AS from becoming a transit system? Answer: Use an outgoing distribution-list to filter all networks not originating from inside the AS

The BGP Synchronization Rule - Do not use or internally a route until the route is learned from a source other than BGP The redistribution command tells the router to take not only routes learned by the source routing protocol but also connected routes on interfaces enabled wit that routing protocol - including ive interfaces. i.e. 1) All routes in the routing table learned by the source 2) All connected routes of interfaces on which the source routing protocol was enabled Delay is configured in tens-of-microseconds Bandwidth is configured in kilobits per second The OSPF Type-E2 metric is simply the metric value listed in the type 5 LSA

To defeat the RIP-OSPF domain loop problem using AD, just configure the AD for OSPF external routes to be higher than the AD of RIP on the same router.

When configuring per-router AD, the IP address of the neighboring router as referenced in the distance command in OSPF configuration will be compared to the RID of router that owns the Type-5 LSA With regards to RIP and EIGRP, the IP address referenced is that of the neighboring router that s the route RIPv2 does not allow summarizing to a mask length that is less than the class full network prefix. To get around the " ip summary-address rip" command issue, create a static route to summarize the routes then redistribute the route using the " redistribute static" command. NOTE: this is not a limitation of RIPv2 but a Cisco IOS implementation issue You might need to issue the " clear ip route* " command on the route you wish to see changes in its routing table when using RIPv2 The istrative distance for a specific routing protocol is locally significant. Using route-maps with PBR, you have two match options to use 1) Match IP address [ ] 2) Match length [min max] When a route-map (with the permit action) matches a packet, the set command defines the action to be taken. The 4 set command options are 1) Set ip next-hop [address 1, address 2........] 2) Set ip default next-hop [....., ....,.........] 3) Set interface [ interface-type interface-number,...........] 4) Set default interface [ interface-type interface-number,...........] N/B: 1) the next-hop IP has to be in the same connected subnet 2) with the default keyword used, the IOS applies the normal destination-based logic first (excluding default routes) To make the IOS process locally generated traffic using PBR logic, the " ip local policy route-map [ ]" global config command should be used

16-Bit ASN Assignment Categories 0 Reserved 1 - 64,495 Assigned by IANA for public use 64,496 - 64,511 Reserved for use in documentation 64,512 - 65,534 Private Use 65,535 Reserved

BGP Operation 1) Only the best route in any BGP update 2) Do not iBGP-learned routes to iBGP peers By default, when a router s a route using eBGP, the advertising router lists its own updatesource IP address as the next-hop address of the route. However when advertising a route to an iBGP peer, the advertising router does not change the next-hop IP address. The "neighbor [A.A.A.A] next-hop self" command changes the default iBGP next-hop behavior

Redistribution of BGP routes into an IGP is generally not recommended. This redistribution requires a relatively large amount of memory and a relatively large amount of processing by the IGP with the much larger number of routes to process. Redistributing the number of routes in the full Internet BGP table could crash the IGP routing protocols. The synchronization features tells a BGP router the following: Do not consider an iBGP-learned route as “best” unless the exact prefix was learned via an IGP and is currently in the IP routing table. Therefore, if you must redistribute eBGP learned routes into an Enterprise IGP, turn synchronization on. This will prevent routing loops Synchronization is applied to the entire BGP process and is "off" by default. Various ways of clearing a BGP neighborship include 1) Reloading the router 2) istratively disabling and re-enabling the BGP neighborship using the neighbor shutdown and no neighbor shutdown commands 3) Various favors of the ip BGP clear exec command N/B: The "clear ip bgp soft in" command only works if the "soft reconfiguration inbound" keyword is added to the "neighbor "command This command causes the router to retain the received BGP updates from that neighbor The newer version of this command (without the "soft in" keyword), doesn't require "soft reconfiguration". It uses the "route refresh" feature (this allows a BGP router to ask its neighbor to resend its full BGP update To use the "show ip bgp neighbor received routes" command, soft reconfiguration inbound has to be configured BGP uses the AS_Path PA as its primary loop prevention tool To display the RID, use the "show ip bgp nlri" exec command The weight can be set using 1) route-map 2) "neighbor A.A.A.A weight" command ( does not use an "in" or " out" direction because weight can only be set on input) Best BGP route tiebreaker Step 9) Oldest (longest known) eBGP route (skip this step if there is no current best path) Step 10) lowest neighbor BGP RID Step 11) lowest neighbor IP address As it turns out, because Updates received from eBGP peers do not include the Local_Pref PA, IOS lists a null value for Local_Pref for eBGP-learned routes by default. However, Updates from iBGP peers do include the Local_Pref. Note that both the "show ip bgp longer-prefixes" command’s briefer output, and the show "ip bgp A.A.A.A/B" commands more verbose output, both identify the Local_Pref value. However, the longer command output does not list the Weight value.

The routing table manager (RTM) decides which of all the best routes will be included in its routing table  eBGP - 20  iBGP - 200  IGPs - various ADs The "show ip bgp rib-failure" command list one line for each best route the RTM didn't place in the routing table (adjust the various default ADs to influence which route is placed in the routing table) Assuming ISPA is preferred, Only when the AS_Path (before prepending) is at least the number of ASNs added shorter through ISPB can the ISPB path be chosen. Note: When using AS_Path prepending, do not prepend just any ASN. BGP still uses the AS_Path for loop avoidance, so using an ASN already in the AS_Path, like the ASN of the most recently added ASN (for example, ASN 3 in this case), or the local ASN (for example, ASN 11 in this case), makes the most sense. Although presented here as a tool for influencing outbound routes, As_Path prepending can also be used to influence the inbound routes as well. Weight is local for each router Local Preference is d to all iBGP peers within the same AS ( by design, this can be set on eBGP peers. They will then the Local_Pref in iBGP updates) The "neighbor x.x.x.x remove-private-as" removes private ASNs from outbound bgp updates bound for the specified neighbor BGP updates can also be filtered based on the AS_Path using: "ip as-path access-list < > [deny|permit] { }" "neighbor x.x.x.x filter-list [out|in]" N/B: for the as-path access-lists, " deny^100$" ; ^ means that the AS Pathetic must begin with the given AS $ means that the path must end with the given AS Find out which represents "contains" Therefore, ^100$ means that the as access-list will match only updates sourced from AS 100 . (Period) denotes a wildcard * stands for repetition Therefore "permit .*" permits any value not matched by the deny access list ( assuming the deny portion came before it) BGP If u decide to use a network from say the ISP as your default route within the enterprise, the "ip defaultnetwork" command works well on the enterprise boarder router only with remotely-learned classful networks. It should not be used with classless networks. An alternative to using the ip default-network command is issuing the neighbor X.X.X.X default-originate configuration on the ISP router. NOTE: By default, the MED is compared only when the route is being received from the same neighboring AS, although d by different border routers. The nondefault behavior of comparing the MED regardless of the AS advertising the route can be activated using the bgp always-compare- med command, however, the results of this command have to be carefully considered. NOTE: Because the MED is an optional attribute, it might not be present in BGP updates. RFC 4271 requires that a missing MED is equivalent to having the MED set to 0. However, a missing MED can also

be considered to be the worst possible MED, which is activated using the bgp bestpath med missing- asworst command. The use of route reflectors is an alternative to using a full mesh internal BGP. The "neighbor x.x.x.x route-reflector-client" which is configured on the route reflector server, reflects or s BGP updates received from its x.x.x.x iBGP peer to other iBGP peers within the ASN The link local addresses for the respective IPv6 tunnels are derived as follows: 1) Manually configured - FF80::/96 with tunnel source IPv4 address 2) GRE - IPv6 eui-64 rule using lowest numbered interface's MAC address 3) Auto 6to4 - FF80::/96 with the tunnel's IPv4 source address 4) ISATAP - FF80::/64 with the embedded IPv4 address in the IPv4 address formed using the modified eui-64 BGP next-hop of 0.0.0.0; 1) The network was locally originated via redistribution of IGP into BGP or 2) A network or aggregate command in BGP configuration When configuring tunnels, IPv4 addresses are not needed on tunnel interfaces ISATAP uses modified eui-64; 0000:5EFE in the 5 & 6 quartet DH Config ip dh pool [pool-name] network x.x.x.x <mask> default-router y.y.y.y ip dh exclude-address z.z.z.z (assuming the default gateway-y.y.y.y is in this range. dns-server a.a.a.a b.b.b.b IPsec tunnels do not IGPs. Alternatives that do include 1) GRE 2) Group Encrypted Transport (GET) 3) Dynamic Multipoint VPN (DMVPN) 4) Virtual Tunnel Interface - same as GRE but does not use a 4 byte header For a given prefix/length, OSPF always prefers an E1 route over an E2 route OSI networking layer addressing is implemented by using two types of hierarchical address 1) Network Service Access Point (NSAP) 2) Network Entity Titles (NET)