CCNP Concepts Flashcards
How do you configure BGP with a loopback?
Use the neighbor 10.0.0.2 update-source command. Without the neighbor update-source configuration command, the TCP session will use the IP address of the outgoing physical interface and the neighbor will reject the incoming TCP SYN packet as it’s not coming from a recognized BGP neighbor.
What do you have to add in OSPF to ensure route redistribution works?
You must add the subnets parameter otherwise OSPF will ONLY advertise networks.
Does an implementation plan require the detailed configuration changes to be made?
It may seem trivial for simple implementations, but Cisco requires that any network implementation plan includes documentation that shows what changes will be made to the current configurations. When performing more complex implementations in a production environment, having a well though-out implementation plan reduces the downtime and is very important – just make sure you also include the actual configuration change steps!
Explain route map logic.
- If you use an ACL in a route-map permit clause, routes that are permitted by the ACL are redistributed.2. If you use an ACL in a route-map deny clause, routes that are permitted by the ACL are not redistributed.3. If you use an ACL in a route-map permit or deny clause, and the ACL denies a route, then the route-map clause match is not found and the next route-map clause is evaluated
Which router command will allow an administrator to configure the administrative distance of a redistributed routing protocol?
The distance command will manually change the AD value for specific network prefixes.
The syntax is distance {ip-address {wildcard-mask}} [ip-standard-list] [ip-extended-list]
router rip
distance 125 10.10.10.2 0.0.0.0
What special type of IPv6 address does ::/0 represent?
A: ::/0 is the default route in IPv6
The address ::/0 is the IPv6 equivalent of “any”, which is why it is used as the default route address. It is the equivalent of 0.0.0.0/0 in IPv4.
An example IPv6 static default route configuration would look like this:
RouterA(config)# ipv6 route gig0/1 ::/0 10.10.10.2
What are the two ways a BGP router can advertise its networks?
A: A BGP router can advertise its networks using the network statement or the aggregate-address command.
BGP uses network statements to define which networks the local router should advertise. Each network doesn’t have to be originating from the local router, but the network must exist in the routing table. The optional mask keyword is often recommended as BGP supports subnetting and supernetting.
The aggregate-address command can be used to aggregate (or summarize) BGP routes. The aggregate network is then advertised to a router’s BGP neighbor in the same way the network command does – only it contains a larger network that includes many smaller BGP networks.
Which three OSPF LSA types describe subnet information that can be used when calculating routes within OSPF?
A: LSA Type 1, 2, and 3
LSA Types 1, 2, and 3 all are used for calculating the best cost to inter-OSPF routes. LSA Types 4, 5, and 7 are used for calculating the best cost to routes outside of OSPF – those redistributed by another routing protocol.
True or False:When EIGRP detects a topology change, it sends an update to all of its neighbors with only the changes in the update.
A: False
EIGRP sends updates to only to the routers affected by the change, not all of its neighbors. One of EIGRP’s many benefits is that it uses partial triggered updates to its directly connected neighbors rather than periodically sharing its entire routing table. This saves link bandwidth because:
- Updates are only sent if a change is incurred
- Only the changes are sent in the update
- Updates are only sent to a routers’s affected neighbors
An administrator issues the command aggregate-address 192.168.0.0 255.255.252.0 on a BGP router peered with other BGP speakers. They peers do not receive the aggregate network advertisement however. What is most likely the cause?
A: The configured router does not have any 192.168.0.0/22 subnets in its BGP routing table.
The aggregate-address mask command allow an administrator to summarize specific routes into a single aggregate route. Aggregation applies only to routes present in the BGP routing table however. If one or more routes within the aggregate address exist in the BGP routing table, aggregation will be performed.
This is different from the BGP network command, which applies to routes within the local IP routing table.
The following configuration has been applied to redistribute OSPF into EIGRP. What does the value of 1000 represent?
router eigrp 1
redistribute ospf 1 metric 1000 100 255 1 1500
A: The 1000 value in the redistribute command represents a bandwidth value of 1000Kbps, or 1Mbs.
The metric subcommand under EIGRP assigns values to all routes redistributed in to the routing protocol (EIGRP in this case). Different routing protocols use differenet and incompatible metrics to determine the trustworthiness of their routes. When redistribution is performed, a standard set of metrics must be used for the external routes being imported.
In this example, the values represent 1000Kbs of bandwidth, 1000 microseconds of delay (always need to multiply this by ten), a load of 255, a reliability of 1, and 1500 for the MTU.
RouterA and RouterB are EIGRP neighbors. RouterA needs to receive routes from RouterB, but not advertise any routes to RouterB. What would better solve the requirements on RouterA – the passive interface command or using a distribute list?
A: A distribute list would be the best technique to meet the question’s requirements
First, the passive-interface command would not meet the requirements. If the passive-interface command was applied, the neighbor relationship would end because it blocks hellos from being exchanged.
Distribute lists are designed to solve exactly the type of requirements the question presents. They filter what routes are advertised or received.
In this case, a configuration similiar to the following would meet the requirements:
access-list 10 deny any ! router eigrp 100 distribute-list 10 out FastEthernet 0/1 !
What dynamic routing protocol allows an administrator to control how much bandwidth is used for routing protocol control information over a low-speed hub-and-spoke Frame Relay topology
A: EIGRP
By default EIGRP will use up to 50% of a link’s bandwidth for control information. EIGRP can however be configured to only use a specific amount of control-plane bandwidth over the link.
In situations where a hub-and-spoke Frame Relay design is used with lower a low CIR (like 64 kb/s), EIGRP can be configured with the actual CIR value – not just the default serial interface’s physical bandwidth (1544 kb/s). This makes EIGRP a popular choice in legacy, slow speed Frame Relay networks.
An example might look like:
R1 (config)# interface serial 0/0/0
R1 (config-if)# bandwidth 64
R1 (config-if)# exit
What two types of routes do EIGRP stub routers advertise?
A: Summary and connected routes
A router that is configured as a stub with the eigrp stub command shares connected and summary routing information with all neighbor routers by default.
This can be verified in the output of the show ip eigrp neighbor detail command on the hub router (connected to the spoke/stub router).
Based on the OSPF redistribution configuration below, what is the effect of the external 2 parameter?
A: The external 2 parameter adds an extra match condition to the redistribution – looking elusively for OSPF E2 routes.
In this case, only OSPF E2 routes coming from OSPF process ID 1 will be redistributed onto the OSPF 20 process.
router ospf 20
redistribute ospf 1 external 2
True or False: The IPv6 header is 40 bits long.
A: False, the IPv6 header is 40 bytes long
All IPv6 addresses are 128 bits long and contain a fixed-length 40-byte header. Understanding the feilds contained within the IPv6 header is important. Remember that version, traffic class, flow label, payload length, next header, hop limit, SA, and DA are all fields contained within the IPv6 header.
What technique when applied to a router at the boundary of an IPv4 network and an IPv6 network would allow a IPv4-only and IPv6-only hosts to communicate?
A: NAT-PT
Network Address Translation – Protocol Translator (NAT-PT) allows IPv4 devices to communicate with IPv6 devices without running a dual stack requirement on end hosts. NAT-PT allows bidirectional translation services.
Define the MAC address of the multicast IP address 239.255.0.11?
A: 0100:5E7F:000B
When converting multicast IP addresses to their corresponding MAC address, simply keep the following rules in mind.
- The MAC address for multicast addresses always begins with 0100:5E.
- The remaining hex values are derived from the last 23 bits in the IP address.
In this case, we break the 255 octet in half to 127 (7F in hex). The third octet of 0 is 00 in hex. The last octet of 11 is 0B in hex.
An update has been made to the BGP ingress routing policy. Which BGP feature should be used used to process the update while avoiding high memory utilization on the router?
Will BGP apply changes to the routes it already has?
What is another way to do this?
A: Route refresh
Internet routers running BGP have enormous routing tables. When a filter is applied, like a route map, changes to BGP attributes occur. Those changes could affect many of the routes already in the routing table from BGP. Because BGP’s network list is usually very long, applying a route map or prefix list after BGP has converged can be disastrous. The router would have to check the filter against every possible route and attribute combination.
To make matters worse, if it were to apply the filters and pull routes back from neighbors, those changes could then cause another reconvergence – and on and on. In an effort to avoid that scenario (BGP loves stability), BGP will only apply attribute and network changes to routes AFTER the filter has been applied. All existing routes stay unchanged.
There are two ways to reset the BGP session without resetting the TCP sessions between all peers: route refresh or soft-reconfiguration.
When a route refresh is perfomed, the BGP router requests its remote peers to resend its BGP Adj-RIB-Out. This allows the BGP router to reapply the inbound policy without any added memory overhead on the local router.
Soft-reconfiguration stores all received (inbound) routing policy updates without modification in a table so that when a new filter is applied, the router will use this table to calculate the changes without resetting the TCP session between the two BGP peers. This is extremely memory intensive and not recommended by Cisco.
The show ip ospf database external shows what type of LSAs?
A: Type 5 LSAs
The show ip ospf database external command displays information about external LSAs (Type 5 LSAs) only.
OSPF uses the Type 5 external link LSAs to advertise external routes originated from an ASBR. They are flooded through the OSPF domain and directs packets for those external addresses to the ASBR.
DOCSIS is the international standard for transmitting data over what type of system?
A: Cable
DOCSIS, or Data Over Cable Service Interface Specification, is is an international telecommunications standard that enables high-speed data transfers over traditional cable TV networks. It is used commonly by cable TV providers to deliver internet connectivity to home and businesses over coax.
What three parts make up a complete and functional Cisco IP SLA operation?
A:
- The operation number
- The operation definition
- The operation schedule (start time)
All three parts are required for a Cisco IP SLA operation to function. A short example with each requirement on one line would be:
ip sla 20
icmp-echo 10.20.1.1
ip sla schedule 20 start-time now life forever
What would be the result if two OSPF routers were directly connected over a shared segment and the priority on both were set to 0?
A: Both routers would remain stuck in the two-way state
For proper OSPF exchange to take place over a share segment, a DR and BDR must be elected. Since both routers in this example have their OSPF priority set to 0, neither can become the DR and therefore the OSPF exchange will stop.
OSPF Elections
1. When the OSPF process on a router starts up, it listens for hellos. If it does not receive any within its dead time, it elects itself the DR.
- If hellos are received before the dead time expires, the router with the highest OSPF priority is elected as the DR. Next, the same process happens to elect the BDR. Note: If a router’s OSPF priority is set to 0, it will not participate in the elections.
- If two routers happen to have the same OSPF priority, the router with the highest Router ID will become DR. The same is true for BDR.
RouterA needs to establish a BGP neighbor relationship with RouterC in a way that allows failover if either RouterB or RouterD goes down. How can this be accomplished? (Non fully meshed square)
A: Configure loopback interfaces on RouterA and RouterC and use them in the BGP update-source command.
Instead of using one physical interface to establish a TCP connection to a BGP peer, loopbacks on each router can be used to establish the connection. This decouples the TCP/IP connection from a single physical interface, allowing link redundancy.
RouterA: interface loopback0 ip address 1.1.1.1 255.255.255.255 ! router bgp 65001 neighbor 2.2.2.2 remote-as 65001 neighbor 2.2.2.2 update-source loopback0
RouterC: interface loopback0 ip address 2.2.2.2 255.255.255.255 ! router bgp 65001 neighbor 1.1.1.1 remote-as 65001 neighbor 1.1.1.1 update-source loopback0
True or False: When a system is running in dual stack mode, the IPv6 stack has a dependency on the IPv4 stack to operate.
A: False
IPv4 and IPv6 can run on the same host or system with no dependency on each other to function. When both IPv4 and IPv6 are run in parrallel, it is refered to as a dual stack arcitecture. As organizations begin to migrate their networks to IPv6, dual stack can be used to transition those hosts that support it.
Dual Stack Benefits
- IPv4 and IPv6 can run independent of each other
- Dual stack removes the IPv6-in-IPv4 tunneling requirement
- Dual stack allows a slower, managed migration off of IPv4
Out of all of the IPv6 migration strategies, dual stack is often preferred. Since the end devices can speak to each other in either IPv4 or IPv6 natively, either can be used.
Perhaps the best part? The protocol choice can be controlled in DNS. The transmitting host will send IPv4 packets if it receives an IPv4 address from the DNS server (known as an A record) or IPv6 packets if it receives an IPv6 address from DNS (known as an AAAA record).
Changing which hosts uses which IP protocol can simply be a matter of updating the DNS A or AAAA record.
RouterA, an ABR between area 0 and area 2, has routes in area 2 for 10.20.1.0/24 and 10.20.2.0/24. 10.20.1.0/24 has a metric of 16 and 10.20.2.0/24 has a metric of 34. If the statement shown below is added to the running configuration of RouterA, what new route will be advertised into area 0?
A: RouterA will advertise a route to 10.20.0.0/16 into area 0 with a metric of 16
The area 2 range 10.20.0.0 255.255.0.0 command creates a summary route for the 10.20.0.0/16 network. By default OSPF summary routes use the metric of the lowest metric route as its own (16 in this case).
Note also that RouterA will stop advertising routes to the 10.20.2.0/24. and 10.20.1.0/24 networks into area 0.
Router R1 has been recently configured for EIGRP MD5 authentication, but it appears that the EIGRP packets are being dropped by R1′s neighbors. The password has been double-checked to match the other routers. What should be changed in the configuration below?
R1(config)# key chain SECURE
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string daffy
R1(config-keychain-key)# exit
R1(config)# interface gig 1/2
R1(config-if)# ip authentication mode eigrp 10 md5
A: The interface subcommand ip authentication key-chain eigrp 10 SECURE is missing
EIGRP supports authentication of its messages using an MD5 hash. When configured, if an incoming EIGRP packet’s hash does not match the local hash, the packet is silently dropped.
Authentication configuration steps:
- Configure a key chain to group the keys.
- Create a key(s) inside the keychain. The router will look inside the keychain and compare the keys against incoming packets.
- Enable authentication and assign a key to an interface.
- Indicate MD5 as the authentication type.
Based on the these steps, the complete configuration should look like this:
R1(config)# key chain SECURE
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string daffy
R1(config-keychain-key)# exit
!
R1(config)# interface gig 1/2
R1(config-if)# ip authentication mode eigrp 10 md5
R1(config-if)# ip authentication key-chain eigrp 10 SECURE
What are two common checks that should be performed when external routes being redistributed into OSPF are not in the OSPF database?
- Check that the subnets keyword is being used in the redistribution statement.
- Check that the ASBR router is not redistributing the external routes into a totally stubby area.
The subnets keyword at the end of the redistribute command is extremely important of you are redistributing subnets. Without this keyword, OSPF will redistribute networks at their classful boundaries – in effect dropping the specific routes from ever reaching the OSPF database.
Totally Stubby Areas do not accept any external routes from non-OSPF sources and they do not accept routes from other areas within their OSPF autonomous system.
How is bandwidth distributed with EIGRP on a pure multipoint (no subinterface) NBMA network?
How do you avoid overloading?
In this configuration EIGRP will divide the configured bandwidth evenly across each virtual circuit. You must ensure that this will not overload each virtual circuit. For example, if you have a T1 access line with four 56K VCs, you should configure the bandwidth to be 224Kbps (4 * 56Kbps) in order to avoid dropping packets. If the total bandwidth of the virtual circuits equals or exceeds the access line speed, configure the bandwidth to equal the access line speed. Note that if the virtual circuits are of different capacities, the bandwidth must be set to take into account the lowest capacity virtual circuit.
For instance, if a T1 access line has three 256Kbps VCs and one 56Kbps VC, the bandwidth should be set to 224Kbps (4 * 56Kbps). In such configurations, putting at least the slow virtual circuit onto a point-to-point subinterface is strongly recommended (so that the bandwidth can be raised on the others).
How is bandwidth distributed for EIGRP on a Pure Point-to-Point Configuration (Each VC on a Separate Subinterface)?
This configuration allows maximum bandwidth control, since the bandwidth can be configured separately on each subinterface, and is the best configuration if the virtual circuits have different capacities. Each subinterface bandwidth should be configured to be no greater than the available bandwidth on the associated VC, and the total bandwidth for all subinterfaces cannot exceed the available access line bandwidth. If the interface is oversubscribed, the access line bandwidth must be divided across each of the subinterfaces. For instance, if a T1 access line (1544 Kbps) has ten virtual circuits with a capacity of 256Kbps, the bandwidth on each subinterface should be configured to be 154Kbps (1544/10) instead of 256Kbps each.
What are the three NBMA (nonbroadcast multiple access) scenarios for EIGRP?
There are three different scenarios for NBMA interfaces.
Pure Multipoint Configuration (no subinterfaces)
Pure Point-to-Point Configuration (each VC on a separate subinterface)
Hybrid Configuration (point-to-point and multipoint subinterfaces)
Answer the following for each:
Must manually define neighbors?
Must elect a DR/BDR?
Must allow pseudo broadcast?
RFC 2328-compliant modes:
Nonbroadcast (NBMA)
Point-to-multipoint
Cisco additional modes:
Point-to-multipoint nonbroadcast
Broadcast
Point-to-point
RFC 2828 compliant modes:
Nonbroadcast:
Must manually define neighbors? Yes
Must elect a DR/BDR? Yes
Must allow pseudo broadcast? No
Point-to-multipoint:
Must manually define neighbors? No
Must elect a DR/BDR? No
Must allow pseudo broadcast? Yes
Cisco additional modes:
Point-to-multipoint nonbroadcast:
Must manually define neighbors? Yes
Must elect a DR/BDR? No
Must allow pseudo broadcast? No
Broadcast:
Must manually define neighbors? No
Must elect a DR/BDR? Yes
Must allow pseudo broadcast? Yes
Point-to-point:
Must manually define neighbors? No
Must elect a DR/BDR? No
Must allow pseudo broadcast? N/A
Page 3-56 in global knowledge book.
What is the MED (Multi Exit Discriminator) attribute in BGP?
Is lower or higher preferred?
MED is an optional nontransitive attribute. MED is a hint to external neighbors about the preferred path into an autonomous system (AS) that has multiple entry points. The MED is also known as the external metric of a route. A lower MED value is preferred over a higher value.
Wich dynamic IPv6 tunnel type uses 0×2002 for the first two bytes of the IPv6 address and the hexadecimal equivalent of the IPv4 address for the remaining four bytes?
A: 6to4 tunnels
6to4 tunnels are similar to the manual tunnel, but set up the tunnel dynamically.
6to4 tunnels use 2002::/16 IPv6 addresses in front of the 32 bit IPv4 address of the edge router – creating a 48 bit prefix. Each router on both sides of the tunnel needs a route to its peer. They only support static and BGP routes, so be careful.
True or False:When an EIGRP router successor router is removed and a FS exists, the neighbor adjacency is removed then DUAL is notified of the change.
A: False
When an EIGRP router successor router is removed and a FS exists, the router goes through a series of processes to transition from the successor route to the feasible successor route. The process is as follows:
- DUAL is notified of the topology change
- The neighbor adjavency is removed
- All topology entries learned from that neighbor are removed
- The FS route is used
All of these steps occur very quickly, allowing EIGRP to dynamically transition the route to the feasible successor with limited network interruption.
What special type of IPv6 address does ::/128 represent?
A: ::/128 represents the IPv6 unspecified address
::/128, which corresponds to 0.0.0.0/32 in IPv4, is referred to as the unspecified address due to its use of all zeros. The unspecified address is used by applications that need to listen on a particular port or interface for incoming connections. It should never be assigned to a host or router interface.
Why would you configure a Cisco router as a PPPoE client?
A: For DSL internet service provider connectivity.
DSL uses the protocol PPP over Ethernet to transfer information between the end client and the provider equipment. Either the end host (like a PC) can be configured with the appropriate PPPoE client software or the local router can be configured to terminate the connection. If the router is used, it can decapsulate the frames and forward them on to end hosts as traditional IP packets – completely transparent to the end users.
RouterA is being used for mutual route redistribution between and EIGRP and OSPF networks. RouterB, one of RouterA’s EIGRP neighbors is missing a few routes in the OSPF domain. What should you check first?
A: Verify that RouterA, the border router, has the missing OSPF routes in its routing table.
The when troubleshooting missing redistributed routes between routing protocols, it is always a good practice to first verify that the router performing the redistribution shows the routes in its routing table.
If it does not, then you should inspect the routing protocol configuration hop-by-hop.
If the routes are in the border router’s routing table, inspect the redistribution configuration.
Which two dynamic routing protocols will continue to receive routing updates on an interface configured as passive?
A: RIP and RIPv2
The passive-interface command controls the advertisement of routing information differently depending on the routing protocol in use. With RIPv1 and RIPv2, the passive-interface command restricts outgoing advertisements only. EIGRP and OSPF drop their neighbor relationship and in doing so no longer send or receive advertisements on a passive interface.
RIP
The passive-interface command prevents the routing from sending multicast updates on the specified interface, but will still listen for incoming updates from RIP neighbors and keep their routes in the local routing table.
EIGRP/OSPF
Interfaces with the passive-interface command applied do not allow any routing updates or hellos out the interface. For EIGRP and OSPF, this means that the router will not form adjacencies with connected routers on that particular port. This essentially stops all outgoing and incoming updates since the neighbor relationship will drop.
If a BGP router has two paths to a destination and weight ans local preference attributes are not configured, what is the next attribute the router will consider to determine the best path?
What is the next-hop?
A: Local Origin
After weight and local preference, BGP considers the origin attribute to determine the best path. If the route originated locally, it will be preferred. A locally originated route will show a next-hop of 0.0.0.0 in the BGP table.
If it was not originated locally, the network with the shortest AS path is chosen. BGP uses the path selection criteria in the following order:
- Highest weight
- Highest local preference
- Choose routes originated locally
- Path with the shortest AS path
- Lowest origin code ( i
Which of the following are not valid optional OSPF interface configuration parameters? What do each mean? What are their defaults?
database-interval ip ospf dead-interval ip ospf hello-interval flood interval ip ospf retransmit-interval
A: database-interval aand flood-interval are not optional OSPF interface configuration parameters
ip ospf dead-interval
Sets the interval at which hello packets must not be seen before neighbors declare the router down.
ip ospf hello-interval
Specifies the interval between hello packets sent on the interface.
ip ospf retransmit-interval
Specify the time between link-state advertisement (LSA) retransmissions for adjacencies belonging to the interface.
What is synchronization, and how does it influence BGP routes installed in the IP routing table?
A. If your AS passes traffic from another AS to a third AS, BGP should not advertise a route before all routers in your AS learn about the route via IGP. BGP waits until IGP propagates the route within the AS and then advertises it to external peers. A BGP router with synchronization enabled does not install iBGP learned routes into its routing table if it is not able to validate those routes in its IGP. Issue the no synchronization command under router bgp in order to disable synchronization. This prevents BGP from validating iBGP routes in IGP.
When issuing the show ip bgp command, you notice 0.0.0.0 as the next-hop for a network. What two ways could the network have been originated that would make 0.0.0.0 appear as the next-hop address?
A: The network was redistributed into BGP from an IGP or the network was originated from a aggregate or network command.
The fifth column shows the next hop address for each route. A 0.0.0.0 indicates the local router originated the route. This could include a network command entered locally or a network an IGP redistributed into BGP on the router.
Path is frequently ?.
Which routing protocol(s) require a metric to be assigned when redistributing routes from other routing protocols?
A: RIP, IGRP, and EIGRP require a metric to be assigned when redistributing routes into them
When you redistribute one protocol into another, remember that the metrics of each protocol play an important role in redistribution. Each protocol uses different metrics. For example, the Routing Information Protocol (RIP) metric is based on hop count, but Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) use a composite metric based on bandwidth, delay, reliability, load, and maximum transmission unit (MTU), where bandwidth and delay are the only parameters used by default.
RIP IGRP, and EIGRP all require a metric be manually configured for routes redistributed into them. In OSPF, if a metric is not specified, OSPF puts a default value of 20 when redistributing routes from all protocols except Border Gateway Protocol (BGP) routes, which get a metric of 1. For IS-IS, if no metric is specified, a metric value of 0 is used by default.
Which neighbors in the show ip bgp summary output have established a peering relationship with RouterA?
RouterA#show ip bgp summary
BGP currently operating:
AS: 100
Router ID: 10.10.10.10
Cluster ID: 33683901
Neighbor V AS MsgRcvd MsgSent Up/Down State/PfxRcd
- 1.1.1 4 100 11 15 0:09:00 45
- 2.2.2 4 200 27 28 0:23:03 Idle
- 3.3.3 4 200 0 0 0:23:00 Idle
- 4.4.4 4 200 0 0 0:00:27 Active
- 5.5.5 4 300 0 0 0:16:49 31
In the show ip bgp summary output, established peers will show a number under the State/PfxRcd column referencing the number of prefixes received from the neighbor router. Depending on the IOS version, sometimes it will appear as “Estab”.
Idle indicates that the peer is not actively trying to peer. Active indicates that the router is actively trying to establish a peering relationship.
What is the default administrative distance for EIGRP external routes?
A: 170
The default administrative distance for EIGRP external routes in Cisco IOS is 170. The default administrative distance for EIGRP internal routes is 90.
Other default AD values: RIP: 120 OSPF internal: 110 OSPF external: 110 iBGP: 200 eBGP: 20 Connected: 0 Static: 1
Based on the configuration below, how does the distribute-list effect communication with neighbor 10.10.10.2?
router bgp 65001
neighbor 10.10.10.2 remote-as 100
neighbor 10.10.10.2 distribute-list 110 in
!
access-list 110 permit ip 172.16.89.0 255.255.255.0 0.0.0.0
A: The local router will only allow route 172.16.89.0/24 from BGP neighbor 10.10.10.2
Distribute lists are access lists applied to the routing process, determining which networks are allowed into the routing table or included in updates. They essentially act as a filter.
In this case, the distribute-list is applied in the inbound direction to neighbor 10.10.10.2. The distribute-list filter references ACL 110, which permits the route 172.16.89.0/24 and denies all others.
router bgp 65001
neighbor 10.10.10.2 remote-as 100
neighbor 10.10.10.2 distribute-list 110 in
!
access-list 110 permit ip 172.16.89.0 255.255.255.0 0.0.0.0
What type of address does OSPFv3 use to establish neighbor adjacencies?
What is its address block?
A: OSPFv3 uses link-local addresses to establish neighbor adjacencies
fe80::/10
OSPFv3 is an updated version of OSPF designed to accommodate IPv6 natively. OSPFv3 uses the multicast address FF02::5 and FF02::6, but like EIGRP it uses its link-local address as the source address in advertisements.
RouterA is directly connected to two ISP routers (10.10.10.2 and 20.20.20.2) via BGP. Based on the configuration below, which ISP router will Router A use?
A: ISP router 10.10.10.2
On Cisco routers, weight is the most influential BGP attribute. The weight attribute is proprietary to Cisco and is normally used to select an exit interface when multiple paths lead to the same destination. Weight is local and is not sent to other routers. It can be a value between 0-65,535. 0 is the default.
We can see that the weight was set to 100 for neighbor 10.10.10.2, meaning RouterA will prefer that path. The weight to 20.20.20.2 would be the default of zero since none was explicitly configured.
