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CCIE R&S - IP Route
CCIE R&S - Written - IP Routing
| Question | Answer |
|---|---|
| Describe the 5 step process of packet routing. | 1) Router receives frame, checks FCS 2) Ether type check, packet extracted 3) Destination address checked against routing table 4) Router updates IP TTL and checksum 5) Adjacency info learned from lookup used to create new Data Link layer encapsulation |
| Describe 3 drawbacks of Fast Switching. | First packet in every flow must be process switches, cache entry per destination, only supports per-destination load-balancing |
| What is the main benefit of CEF of fast switching? | One entry per prefix instead of per-destination |
| How does Inverse ARP work? | Interface receives LMI PVC Up message, begins to announce its own IP address over the PVC |
| In a classful network, what does a router that has a default route do with a packet who's destination address subnet is not found in the routing table when the packet's corresponding classful network is in the routing tablet? | Discard it |
| What additional step does a Multilayer Switch have to take when routing a packet using VLAN interfaces? | Look up next hop's MAC in CAM table |
| When using a routed Port-Channel, which load-balancing technique should be used? | Layer 3 |
| What are the 5 components of the EIGRP metric? | Bandwidth, Delay, Load, Reliability, and MTU |
| The name for the EIGRP cost between the local router and the destination prefix | Feasible Distance |
| The name for the EIGRP cost that the next hop is advertising to the local router | Advertised Distance |
| What the EIGRP feasibility check rule? | the AD of the next hop router must be less than the FD of the current successor |
| What does the EIGRP status code Passive mean? | network available |
| What does the EIGRP status code Active mean? | network unavailable |
| What does the EIGRP status code Update mean? | network is being updated |
| What does the EIGRP status code Query mean? | outstanding query |
| What does the EIGRP status code Reply mean? | generating a reply to a query |
| What does the EIGRP status code SIA mean? | convergence problem |
| What are the two ways to limit the scope EIGRP queries? | stub or summarization |
| What is an EIGRP SIA Query? | special query to make sure peer relationship is still valid |
| What protocol number does EIGRP use? | 88 |
| What is the EIGRP default hello and hold-timer of fast and slow links? | Fast - 5, 15 ; Slow - 60, 180 |
| What is the EIGRP update destination address? | 224.0.0.10 |
| Does the EIGRP hold time change when the hello time is changed? | No |
| What protocol does EIGRP use to send update messages? | Reliable Transport Protocol (RTP) |
| How are EIGRP retransmissions sent? | Unicast to the neighbor that didn't acknowledge |
| What 4 conditions must be true in order for EIGRP neighbors to form? | K values, Believe they're on same subnet, authentication, and AS number |
| How does a EIGRP router determine which timers to use? | They use the timers that were sent to them by their neighbor |
| Which EIGRP bandwidth value is used in DUAL? | Lowest link speed in the path (kilobits) |
| Which EIGRP delay value is used in DUAL? | Cumulative path delay in 10s of microseconds |
| What is the EIGRP simplified formula? | 256 * [(10^7/ bandwidth) + delay] |
| Which two EIGRP messages do not require acknowledgments? | Hello and ACK |
| If an EIGRP route is stuck in active, what happens to the relationships of neighbors that didn't respond to the query? | They are brought down |
| What is an EIGRP active timer? | Limits the time that a route can stay active |
| If an EIGRP router with a summary address configured receives a query from a neighbor for a more specific route, how does the router respond? | Immediately replies that it doesn't have the route |
| What timer does an EIGRP route start when it sends a reliable message to a neighbor? | Retransmission Timeout (RTO) |
| What does an EIGRP acknowledgement consist of? | One window size message with a sequence number |
| What are the three EIGRP input events? | New routing updates, interface failure, and neighbor failure |
| What are the two EIGRP local computation choices? | Use feasible successor routes or actively query neighbors |
| When a EIGRP router queries its neighbors, what does it do next? | Wait until it receives all replies before it makes a decision |
| How many equal paths can EIGRP load-balance across? What is the default? | 6, 4 |
| What does an inbound EIGRP filter prevent? | Routes from entering the EIGRP topology table |
| Which IP protocol does OSPF use? | 89 |
| Which OSPF message type is a brief version of each LSA? | Database Description (DD or DBD) |
| Which OSPF message type identifies one or more LSAs the send would like to receive? | Link-State Request (LSR) |
| Which OSPF message type contains fully detailed LSAs? | Link-State Update (LSU) |
| Which OSPF message type confirms receipt of a LSU? | Link-Sate Acknowledgement (LSAck) |
| What are the three authentication types in OSPF? | Type 1 - none, Type 2 - Clear Text, Type 3 - MD5 |
| How is authentication configured on OSPF virtual links? | The authentication parameter is added to the end of the area X virtual-link command |
| What are the 6 requirements for OSPF neighbors to form? | Authentication, Subnet and Mask, Area, Area Type, Different RIDs, Hello and Dead Timers |
| What is the OSPF default hello and dead timers for fast and slow links? | Hello - 10 (Fast), 30 (Slow) ; Dead - 4 times hello |
| What is the purpose of the OSPF Master? | To send all DDs first |
| How is the OSPF Master elected? | Highest RID |
| How does an OSPF DD receiver acknowledge receipt? | With an identical DD packet back to sender |
| How many OSPF DD packets are sent at a time and how often? | 1 packet at a time, doesn't send next packet until previous one is acknowledged |
| How does an OSPF router determine which LSA is the newest? | Sequence numbers |
| What happens if the OSPF sequence number gets to 0x7FFFFFFF? | The sequence starts over at 0x80000001 and the LSA must be flooded again |
| What two ways can a OSPF LSU be acknowledged? | Repeating received LSA to sender, LSAck with LSA headers |
| How does an OSPF DR acknowledge receipt of an non-DR DD? | Unicast DD |
| How do OSPF non-DRs acknowledge received multicast DD packet? | Unicast DD |
| In OSPF, what is the difference between neighbors and adjacency? | Neighbors means only the neighbor requirements have been met, Adjacency means both neighbors have completed the database exchange process |
| If an OSPF router receives a hello that contains a DR value of 0.0.0.0, what does that mean? | No router has been elected |
| What is the OSPF wait time? | Amount of time OSPF router will wait until it starts the election process, default is the same as the dead time |
| What action does an OSPF router take if it comes online and receives a hello with the DR value of a RID? | It will skip the election process and assume the DR value is correct |
| Is the OSPF DR/BDR process pre-emptive? | No |
| What type of communication does the OSPF neighbor command imply? | Unicast |
| Where can the OSPF neighbor command be configured? | One side or both |
| What two ways can the OSPF priority be set? | Neighbor command or through received Hellos |
| If an OSPF router has a priority for a neighbor configured and receives a higher value from the neighbor in a hello packet, what action will it take? | Change the neighbor statement to match the received hello priority value because it is higher |
| What does each OSPF router add to the received cost? | Outgoing interface cost |
| How is OSPF reference bandwidth measured? | Mbps |
| What is the default OSPF LSR Refresh interval? | 30 minutes |
| What is the default OSPF max age timer? | 60 minutes |
| What is an OSPF stub network? | A network that doesn't have any neighbor relationships |
| What is an OSPF stub router? | A router that will not forward packets to another router |
| How does an OSPF router become a stub router? | Advertise infinite metric for any transit routes |
| What is an OSPF pseudo node? | A logically separate node for transit networks |
| What is the OSPF infinite metric? | (2^24)-1 or 16,777,215 |
| How are OSPF failed routes quickly removed? | Advertising router sets the route's age to max age, causing flooding throughout the AS |
| What is the difference between the two OSPF external metric types? | E1 metric accumulate through the OSPF domain, E2 metrics remain the same as they were redistributed |
| What is the difference between a Summary LSA and a LSA Summary? | A summary LSA is a type 3 LSA. A LSA summary is a header than goes inside a DD packet |
| Name the OSPF route types in order of preference. | Intra-area, Inter-area, E1, E2 |
| How is an OSPF RID chosen (in order of preference)? | Router-ID command, Highest up/up Loopback IP, Highest up/up non-Loopback IP |
| What three ways can routes be filtered in OSPF? | Distribute-list in, Area X filter-list (ABR only), area X range or area X summary-address with 'no-advertise' keyword (ABR or ASBR only) |
| How does an OSPF ABR prevent loops? | Will learn summary LSA from another ABR in non-area 0, but will not advertise it back into Area 0 |
| How does ABRs treat LSAs created by other ABRs that it learns through a non-area 0 when calculating least cost paths? | It ignores them |
| This OSPF router type has all interfaces in one area | Internal Router |
| This OSPF router type has at least one interface in area 0 | Backbone Router |
| This OSPF router type is connected to at least two different areas | Area Border Router (ABR) |
| This OSPF router type has at least one interface in an area and at least one other interface in another autonomous system | Autonomous System Boundary Router (ASBR) |
| Name of LSA Type 1? | Router LSA |
| Name of LSA Type 2? | Network LSA |
| Name of LSA Type 3? | Network Summary LSA |
| Name of LSA Type 4? | ASBR Summary LSA |
| Name of LSA Type 5? | AS External LSA |
| Name of LSA Type 7? | NSSA External LSA |
| This LSA is generated by every router in the area | Router LSA |
| This LSA is generated by the DR | Network LSA |
| This LSA is generated by ABRs | Network Summary LSA |
| This LSA is generated by ABRs to advertise the ASBR | ASBR Summary LSA |
| This LSA is generate by the ASBR | AS External LSA |
| This LSA is generated by the ASBR in a NSSA area | NSSA External LSA |
| Where are Type 1 LSAs flooded? | In the area of origination |
| Where are Type 2 LSAs flooded? | In the area of origination |
| Where are Type 3 LSAs flooded? | Throughout the AS |
| Where are type 4 LSAs flooded? | Throughout the AS |
| Where are Type 5 LSAs flooded? | Throughout the AS |
| Where are Type 7 LSAs flooded? | In the area of origination |
| What is the OSPF Backbone Area responsible for? | Summarization of each area to every other area |
| 3 design rules of OSPF Backbone Area? | Must be area 0, must be contiguous, every non-area 0 must touch area 0 |
| Which LSA types are blocked by a stub area? | 4 and 5 |
| Which LSA types are blocked by a totally stubby area? | 3,4, and 5 |
| Which stub area type doesn't have a default route injected by the ABR? | NSSA |
| This area allows external prefixes from the area ASBR, but restricts other external routes | Totally NSSA |
| OSPF interface command to summarize from one area to another | area range |
| OSPF interface command to summarize from another domain into OSPF | summary-address |
| Name the 7 OSPF network types | point-to-point, point-to-multipoint, point-to-multipoint non-broadcast, broadcast, non-broadcast multi-access, virtual-links, loopback |
| These 2 OSPF network types don't use a DR or BDR, but uses neighbor discovery | point-to-point, point-to-multipoint |
| This OSPF network type doesn't use a DR or BDR, but neighbors have to be manually configured | point-to-multipoint non-broadcast |
| This OSPF network type uses a DR/BDR and uses neighbor discovery | broadcast |
| This OSPF network type uses a DR/BDR , but neighbors have to be manually configured | NBMA |
| This OSPF network advertises its prefix as a host route | Loopback |
| This OSPF feature prevents domain disruptions while processes are restarting | Graceful Restart |
| If there is an incorrect OSPF network type configuration or misconfigured interfaces, what problem would this cause? | neighbor list empty |
| If there is a secondary IP address issue or Layer1/Layer2 problem in OSPF, what could this cause? | neighbor list empty |
| If an ACL is blocking or there is a stub flag mismatch, what problem could this cause in OSPF? | neighbor list empty |
| If there is a Layer3 interface configuration error or area ID mismatch in OSPF, what problem could this cause? | neighbor list empty |
| If there is a timer mismatch or authentication error in OSPF, what problem could this cause? | neighbor list empty |
| If a neighbor statement is misconfigured or unicast doesn't work in the NBMA environment, what OSPF problem could this cause? | Stuck in Attempt state |
| If hellos are being blocked in one direction or the broadcast keyword is missing from the frame-relay map command in OSPF, what problem could this cause? | Stuck in INIT state |
| If multicast is nonfunctional on one side or there is only authentication on one side in OSPF, what problem could this cause? | Stuck in INIT state |
| If all routers have a priority of 0 or there is broken unicast communication in OSPF, what problem could this cause? | Stuck in TWO-WAY state |
| If a neighbor is stuck in EXSTART or there are duplicate Router IDs in OSPF, what problem could this cause? | Stuck in TWO-WAY state |
| What two problems could be presented by a MTU mismatch in OSPF? | Stuck in TWO-WAY state or stuck in LOADING |
| If there is a corrupted link-state request or a MTU mismatch in OSPF, what problem could this cause? | Stuck in LOADING state |
| When does PBR intercept an packet in the routing process? | After packet extraction, but before routing table lookup |
| What 5 parameters can you match traffic for policy routing? | protocol, application, source ip, destination ip, Layer 3 packet length |
| What 3 parameters can you set for Policy Based Routing? | next-hop, output interface, default next-hop |
| This technology is also known as protocol-independent routing optimization (PIRO). | PfR / OER |
| What 4 performance measurements can PfR use? | Packet loss, Response Time, Path Availability, Traffic load distribution |
| How can PfR split subnets? | By injecting a longer match into the routing table |
| What two requirements does PfR have? | CEF enabled, routing protocol operational |
| How does PfR inject routes? | Redistributes tagged static routes |
| What prevents PfR from supporting MPLS? | It can't recognize the MPLS headers |
| What action does a BR take if it no longer receives keepalives from the MC? | It removes any PfR-added routing information |
| What advantage does PfR have over PBR? | It uses performance metrics |
| What are the two core components of PfR? | Master Controller (MC) and Border Router (BR) |
| What are the 5 phases of PfR | Profile, Measure, Apply, Control, and Verify |
| This PfR phase identifies the traffic classes to control? | Profile |
| In this PfR phase, BRs collect statistics and report them to the MC. | Measure |
| What two ways can PfR measure traffic? | Passively or Actively |
| In this PfR phase, acceptable thresholds of performance are defined. | Apply |
| In this PfR phase, the MC uses BR reported information to identify classes or links that are Out Of Policy | Apply |
| In this PfR phase, the MC controls routing protocol decision. | Control |
| In this PfR phase, the MC ensures the changes have brought the network to In-Policy | Verify |
| Where are the learned traffic classes stored during the PfR profile phase? | Monitored Traffic Classes table (MTC) |
| How does PfR learn prefix traffic classes? | NetFlow Top talker feature |
| How does PfR learn application traffic classes? | the 'protocol' command |
| What 5 states are there in the PfR measure phase? | Default, Choose Exit, Hold-down, In-Policy, Out-of-Policy |
| How is passive measuring done in PfR? | NetFlow |
| How is active measuring down in PfR? | IP SLA |
| How can the apply phase ensure that the network is not unstable as a result of PfR? | Timers |
| How are policies configured in PfR? | oer-map |
| In what 3 ways are routing changes initiated in PfR? | a traffic class goes OOP, an exit link goes OOP, or a period timer expires and traffic classes are in 'choose exit' state |
| In what 4 ways are routing changes actually made in PfR? | IGP metric change, BGP attribute change, route injection, or PBR |
| What does the PfR verify phase rely on? | NetFlow |
| In what two ways can BGP change its advertised distance? | distance bgp (sets defaults), distance (matches routes) |
| What are the four BGP messages? | Open, Notification, Update, Keepalive |
| What is the default BGP keepalive and hold timers? | 60 (keepalive), 180 (hold) |
| When are BGP open messages sent? | Once TCP connection is established |
| What two components are in a BGP open message? | sender's RID, keepalive message |
| What does the router do if BGP timers are mismatched? | Uses the lowest values |
| What is the use of BGP notification messages? | Causes a neighbor relationship to be reset |
| What are the three main fields of a BGP update message? | Withdrawn routes, path attributes, prefix and length |
| When are BGP update messages initially sent? | After peer relationship reaches established state |
| What determines how many BGP update message are sent? | One set per peer group, one update message per PA set |
| When does BGP reach the established state? | Once open messages have been successfully exchanged |
| What command is used to temporarily disable a BGP neighbor? | neighbor X.X.X.X shutdown |
| What is required for the BGP show ip bgp neighbor X.X.X.X received-routes command to work? | soft-configuration |
| What output does the BGP command show ip bgp neighbor X.X.X.X received-routes produce? | All routes received by neighbor, even if locally filtered |
| What output does the BGP command show ip bgp neighbor X.X.X.X advertised-routes produce? | All advertised routes without any PA changes |
| What types of authentication does BGP support on Cisco IOS? | MD5 only |
| What 4 checks does a router go through when receiving a TCP request from a potential BGP neighbor? | 1) TCP request from source IP configured in local neighbor command, 2) ASN of received packet match local neighbor command, 3) Different RID, 4)Authentication |
| What happens if two potential BGP neighbors have mismatched IP addresses? | Settle into an active state |
| What are the 6 BGP neighbor states? | Idle, Connect, Active, Open Sent, Open Confirm, Established |
| Produce BGP neighbor state table. | Idle: Listen for TCP? No; Connect: Listen for TCP? Yes; Active: Listen for TCP? Yes, Initiate TCP? Yes; Open Sent: Listen for TCP? Yes, Initiate TCP? Yes, TCP up? Yes, Open Sent? Yes; Open Confirmed: Listen for TCP? Yes, Initiate TCP? Yes, TCP up? Yes, Op |
| What is the default TTL for eBGP and confederation eBGP packets? | 1 |
| What does BGP actually advertise? | PAs with a set of NLRI that share same values |
| What is a Network Layer Reachability Information (NLRI)? | IP prefix and prefix length |
| What does the network command do in BGP? | Checks current IP routing table for match to add to BGP table |
| What happens if a network advertised by the bgp 'network' command disappears from the IP routing table? | route removes NLRI from BGP table and notifies neighbors via Update to withdraw routes |
| If auto-summary is enabled and the redistribute command is used in BGP to inject a component route, what is advertised? | Classful network |
| If auto-summary is enabled and the network command is used in BGP to inject a component route, what is advertised? | The component subnet |
| If auto-summary is enabled and the network command is used in BGP to inject a classful route, what is advertised? | The classful subnet |
| When IGP routes are distributed into BGP, what happens to their metric? | BGP sets the Multi-Exit Discriminator (MED) value to the same |
| Name the 4 types of BGP attribute types | Well-known Mandatory, Well-known Discretionary, Optional Transitive, Optional Non-Transitive |
| What is instructions should a BGP router follow for a optional transitive PA? | Silently forward PA |
| What is instructions should a BGP router follow for a optional non-transitive PA? | Remove PA |
| How can you manually change the BGP NEXT_HOP PA? | You can't |
| What type of BGP PA is AS_PATH? | Well-known Mandatory |
| What type of BGP PA is NEXT_HOP? | Well-known Mandatory |
| What type of BGP PA is ORIGIN? | Well-known Mandatory |
| What type of BGP PA is ATOMIC_AGGREGATE? | Well-known Discretionary |
| What type of BGP PA is LOCAL_PREF | Well-known Discretionary |
| What are the 4 components of the BGP AS_PATH PA? | AS_SEQ, AS_SET, AS_CONFED_SEQ, AS_CONFED_SET |
| What is the AS_SEQ of an BGP aggregate address if all component subnets have different AS_SEQ values? | null |
| What is the AS_SEQ of an BGP aggregate address if all component subnets have the same AS_SEQ values? | The same as the component routes |
| When is BGP AS_SET used? | when as-set option configured and AS_SEQ is null |
| What BGP AS_PATH component values are used for AS path length check? | AS_SEQ, AS_SET (only counts as 1 if used at all) |
| When an BGP aggregate is formed, when is 'i' used? | if as-set option is not used, if as-set is used and all component routes use the origin code 'i' |
| When an BGP aggregate is formed, when is '?' used? | When as-set option is used and at least one of the component subnets has an origin code '?' |
| How can BGP use the network command to add a summary route? | Match a static route pointing to null0 |
| What are the three ways to inject a default route into BGP? | network, redistribute with default-information originate BGP command, neighbor X.X.X.X default-originate |
| What is the purpose of the 'route-map' option on the BGP neighbor X.X.X.X default-originate? | To actually check the IP routing table for against a list before advertising default route to neighbor |
| How is the neighbor X.X.X.X default-originate BGP command different from the network and redistribute command? | The neighbor command does not add the route to the BGP table, advertises only |
| What are the two effects of the BGP command network X.X.X.X backdoor? | Changes AD of route to 200, doesn't advertise to any neighbor |
| What additional constraint is placed on a synchronization check if OSPF is the IGP? | OSPF RID and BGP RID of advertising router must be the same |
| What are the BGP private ASNs range? | 64512 - 65535 |
| What three conditions have to be met for BGP Private ASNs to be removed? | 1) Can only remove at the point of sending an eBGP Update 2) Current AS_SEQ can only be private ASNs 3) AS_SEQ cannot contain ASN of neighbor receiving the advertisement |
| What is required for BGP to show changes once a filter is applied? | Clear command |
| What is the limitation of used standard ACLs when matching prefixes in BGP? | Standard ACLs cannot match network mask length |
| What is the meaning of the regular expression '^'? | start of line |
| What is the meaning of the regular expression '$'? | end of line |
| What is the meaning of the regular expression '|'? | logical or |
| What is the meaning of the regular expression '_'? | delimiter (blank, comma, start, or end of line) |
| What is the meaning of the regular expression '.'? | any single character |
| What is the meaning of the regular expression '?'? | zero or one of the preceding character |
| What is the meaning of the regular expression '*'? | zero or more of the preceding character |
| What is the meaning of the regular expression '+'? | 1 or more of the preceding character |
| What is the meaning of the regular expression '(string)'? | characters inside are a single entity |
| What is the meaning of the regular expression '[string]'? | matches any single character inside |
| What is required for BGP neighbors to receive community values? | neighbor X.X.X.X send-community' configured on sending router |
| What type of list is a BGP community list? | Unordered |
| What two types of community lists are available for use with BGP? List ranges? | Standard (1-99), Extended (100-199) |
| What additional features do extended community lists support in BGP? | matching with regular expressions, allows more than 16 lines in a single list |
| What is the show ip bgp regex command equivalent for communities in BGP? | show ip bgp community-list N |
| What restraint is there on setting the comm-list (delete) on a route-map in BGP? | comm-list can only contain one string of communities |
| What is the value of the NO_EXPORT community in BGP? | FFFF:FF01 |
| What is the value of the NO_ADVERT community in BGP? | FFFF:FF02 |
| What is the value of the LOCAL_AS or NO_EXPORT_SUBCONFED community in BGP? | FFFF:FF03 |
| What behavior should a router use if it receives a NLRI that has the community value of FFFF:FF02? | Not advertise it anywhere else |
| How does the BGP table list routes? | From newest learned to oldest |
| What BGP weight is assigned to all routes locally injected? | 32,768 |
| In what two ways does confederation peers from different sub-Ass mimic eBGP? | TTL of 1 for confederation-to-confederation connections, AS_CONFED_SEQ checked for loops |
| How does the BGP command bgp always-compare-med change the decision process? | By default, multiple routes to same network with MED values from different neighboring ASNs are ignored, this command compares them regardless of the neighboring ASN values |
| How does the BGP command bgp deterministic-med change the decision behavior? | By default, Cisco routes compares the first two newest routes in the list, picks a winner, then compares that winner with the rest of the list. This command changes so that the best routes per adjacent AS are chosen and then compared |
| Why would the BGP command bgp bestpath compare-routerid be used? | To consider RID for external peers (iBGP peers' RIDs are considered by default) |
| What three things have to be true for BGP to consider adding more than one path to a network to the IP routing table? | Decision process has to get past step 8 (best IGP metric to next hop), maximum-paths (eBGP) or maximum paths ibgp (iBGP) value has to be greater than 1, eBGP routes have to have same adjacent ASN or iBGP routes have to have different NEXT_HOP values |
| Where is the BGP command maximum-paths eibgp used? | MPLS only |
| What is the limit of the number of best paths BGP can have for a single prefix? | 1 |
| Which protocol and port number does BGP use? | TCP 179 |
| eBGP peers are assumed to be ________________. | directly connected |
| What are the 3 solutions for the 'iBGP Split-Horizon' rule? | Route Reflector, Confederations, or Fully Meshed Peers |
| What two commands are necessary on a confederation border router? | bgp confederation identifier and bgp confederation peers |
Created by:
ajballer15
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