Term
| What are the new LSAs used with OSPTv3 and IPv6? |
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Definition
- Link LSA - describes a router's local link address and a list of IPv6 prefixes associated with the link. This LSA is flooded to the local link only
- Inter-area-prefix LSA - describes routes to IPv6 prefixes that belong to other areas. Similar to OSPFv2 type 3 summary LSAs. These originate from the ABR and flood with the area only.
- Intra-area-prefix LSA - used to advertise IPv6 prefixes associated with a router, a stub network, or an associated transit network segment. |
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Term
| With link-state routing protocols, how ofter is the routing table refreshed if no updates other than hello messages have been sent? |
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Definition
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Term
| When is the only time that a static route is not used on an outbound interface? |
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Definition
| When an outbound interface goes down. A static route will not be used because it will be removed from the routing table. |
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Term
| Describe the 2 ways how route redistribution can be accomplished. |
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Definition
- One-way redistribution only allows redistribution from one routing protocol to another. Normally used in conjunction with a default or static route at the edge of the network.
- Two-way redistribution is where routing information is exchanged between both routing protocols. |
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Term
| What are the different type of LSA messages produced by OSPF? |
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Definition
- Type code 1, router LSA - produces by every router and flooded within a single area. Includes all the router's links, interfaces, state of links, and cost
- Type code 2, network LSA - produced by every designated router on every broadcast or NBMA network. It lists all the routers in the multi-access network. This type is contained within an area
- Type code 3 summary LSA for ABR - produces by ABR and sent into an area to advertise destinations outside the area
- Type code 4, summary LSA for ASBR - produced by ASBR and sent into an area by the ABR to advertise the ASBR
- Type code 5, AS external LSA - advertises destinations external to the OSPF AS, flooded throughout the whole OSPF AS
- Type code 7, not-so-stubby area (NSSA) external LSA - originated by ASBR in an NSSA. It is not flooded throughout the entire OSPF AS, only the NSSA |
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Term
| Describe the use of OSPF virtual links |
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Definition
| You can use virtual links to temporarily connect (virtually) an area to the backbone. The flow of the virtual link is unidirectional and must be configured in each router of the link. |
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Term
| Describe the local preference attribute of BGP |
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Definition
| The local preference attribute indicates which path to use to exit the AS. It's a well-known discretionary attribute between iBGP peers and is not passed on to the external BGP peers. The higher preference is always preferred (default=100) |
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Term
| Describe the next-hop attribute of BGP. |
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Definition
| The next-hop attribute is the IP address of the next IP hop that will be used to reach the destination. The next-hop attribute is a well-known mandatory attribute. |
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Term
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Definition
| IS-IS was intended to route OSI connectionless network protocol. It create 2 levels of hierarchy. Level 1 for intra-area and level2 for inter-area routing. Level 1 IS's communicate with other level 1 IS's in the same area. Level 2 IS's (routers) are configured for L1/L2 areas, which route between level 1 area and form an inter-domain routing backbone |
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Term
| Describe the MED attribute in BGP |
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Definition
| The MED attribute tells external BGP peers the preferred path into the AS when multiple paths to the AS exist. It is an optional non-transitive attribute carried in eBGP updates. The MED attribute is not used with iBGP peers. The lowest value is preferred and the default is 0 |
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Term
| What are the 4 timers used by RIPv1? |
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Definition
- Update - 30 seconds
- Invalid - 180 seconds
- Flush - 240 seconds
- Holddown - 180 seconds |
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Term
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Definition
| iBGP is the term used to describe the peering between BGP neighbors in the same AS. iBGP is used primarily in transit autonomous systems, which forward traffic from one external AS to another external AS |
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Term
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Definition
| eBGP is used to describe BGP peering between neighbors in different autonomous systems. The eBGP peers need to share a common subnet |
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Term
| How many updates can be stored in one RIPv1 update message? |
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Definition
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Term
| Explain how route feedback occurs? |
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Definition
| Route feedback occurs when a routing protocol learns from another routing protocol and them announces the routes back to the routing protocol. |
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Term
| Describe the AS path attribute in BGP |
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Definition
| The AS path is a well-known mandatory attribute that contains a list of the AS numbers in the path to the destination. Each AS prepends its own AS number to the AS path. The AS path describes all the autonomous systems that a packet would have to travel to reach the destination IP network. When the AS attribute is used to select a path, the route with the fewest AS hops is preferred |
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Term
| Which routing protocols are considered hierarchical and which are consider flat? |
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Definition
Flat = RIPv1 and 2, IGRP. EIGRP is considered a flat routing protocol, but it can be configured with manual summarization to support hierarchical designs.
Hierarchical = OSPF and IS-IS |
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Term
| What type of authentication can be used on a router using OSPFv2? |
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Definition
| You can use 64-bit clear text or MD5. The passwords don't need to be the same throughout the area, but they do need to be the same between neighbors. |
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Term
| What are some differences between OSPFv3 and OSPFv2? |
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Definition
| OSPFv3 is for IPv6 networks only and that its not backward-compatible with OSPFv2 (used for IPv4). OSPFv3 uses multicast group FFo2::5 for all OSPF routers and FF02::6 for all designated routers. |
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Term
| What are the 4 components that characterize EIGRP? |
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Definition
- Protocol-dependent modules- independent support for IP, IPX, and APPLETALK
- Neighbor discovery and recovery - hello/holddown timers are 5/15 seconds for high-sped links and 60/180 seconds for low-speed links
- Reliable transport protocol (RTP) - used to manage EIGRP packets
- DUAL - used to calculate a best path and 2nd best path (successor and feasible successor) |
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Term
| What are the different AS external path types for OSPF? |
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Definition
- Type 1(E1) - external routes that have a metric that is the sum of the redistribution cost plus the cost of the path to reach the ASBR
- Type 2(E2) - external routes which is the metric (cost) used in the redistribution. |
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Term
| Describe an OSPF stub area |
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Definition
| You can configure a area as a stub area to prevent OSPF external LSA (type5) from being flooded into that area. A single default route is injected into that area instead. If multiple ABRs exist in the stub area, all inject the default route. |
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Term
| How do confederations work in reducing the iBGP mesh? |
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Definition
| With confederations, the AS is divided into smaller, private autonomous systems and the whole group is assigned a confederation ID. The private As numbers or identifiers are not advertised to the internet but are confined within the iBGP networks. Each private AS is configured with eBGP to communicate with other semi-autonomous systems in the confederation. External ASs see only the AS number of the confederation and this number is configured with the BGP confederation identifier. |
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Term
| What are the 2 possible states that an EIGRP route entry can be in? |
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Definition
- Passive state - In passive state when the router is not performing any recalculations for the entry (P). If a successor goes down and a route entry has a feasible successor, the router does not need to preform any recalculations
- Active state - DUAL places the route entry for a destination in active state if the successor goes down and there is no feasible successor. The router then queries neighbors for a feasible successor, till the active timers (3 minutes) expires. |
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Term
| what are the different types of packets used by EIGRP? |
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Definition
- Hello - for discovering neighbors, using multicast 224.0.0.10
- Acknowledgment - acknowledgment for the receipt of an update packet. Contains not data and is only sent to the sender of the update packet.
- Update - Contains routing information for destinations. EIGRP unicasts update packets to newly discovered neighbors or multicasts regular updates
- Query - used to find a feasible successor ro a destination
- Reply - response to a query packet, providing a feasible successor. Sent only to the query sender |
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Term
| What are the different route types for a router when using OSPF? |
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Definition
- Internal router - any router who's interfaces all belong to the same OSPF area. They keep only 1 link-state DB
- ABR - routers that are connected to more than 1 area. These routers maintain a link-state DB for each area they belong to. Also generate summary LSAs
- ASBR - routers that inject external LSAs into the OSPF DB (redistribution). These external routes are learned via other routing protocols or static routes.
- Backbone router - routers with at least one interface attached to area 0 |
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Term
| What are some of the changes made to OSPFv3 from OSPFv2? |
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Definition
- Per-link processing - OSPFv2 used per-subnet processing. With link processing, routers in the same link can belong to multiple subnets
- Address semantics removed - addresses are removed from the router and network LSAs. The LSAs now provide topology information
- No authentication - OSPFv3 used the authentication schemes inherited with IPv6
- New link LSAs - For local-link flooding scope
- New intra-area-prefix LSA - carries all the IPv6 prefix information. Similar to OSPFv2 router and network LSAs |
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Term
| Before 2 BGP routers can exchange routing updates, what information needs to be exchanged? |
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Definition
| BGP version number, AS number, BGP router ID, and BGP capabilities |
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Term
| Explain how IGMP snooping works |
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Definition
| IGMP snooping listens for IGMP messages between the hosts and routers. If a host sends an IGMP query message to the router, the switch adds the host to the multicast group and permits the port to receive multicast traffic. The port is removed from the multicast traffic if the host sends an IGMP leave message to the router. |
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Term
| Explain the difference between spare and dense multicast routing protocols. |
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Definition
- Dense MRPs flood the traffic throughout the network and then, at the request of the receiving routers, stop the flow of traffic on the branches of the network which have no members of the multicast group.
- Spare MRPs do not send traffic until it is requested by the receiving hosts or routers. |
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Term
| Describe how priority-based routing (PBR) is used in route manipulation |
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Definition
| You can use PBR to modify the next-hop address of packets or to mark packets to receive differential service. PBR is commonly used to modify the next-hop address based on the source address. You can also use PBR to mark the IP precedence bits in outbound IP packets so that you can apply QoS policies. |
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Term
| Describe how weight is used with BGP |
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Definition
| Weight is assigned locally on a router to specify a preferred path if multiple paths exist out of a router for a destination. Weight can be applied to individual routes or to all routers received from a peer. Weight is specific to Cisco routers and is not propagated to other routers. |
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Term
| How does iBGP use route reflectors? |
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Definition
| Since iBGP requires that all routers be configures with local links to all other iBGP routers, some routers can use route reflectors and serve other routes that act as route-reflector clients. Route reflectors allow a router to advertise or reflect routes to clients. All client routers in the cluster peer with the route reflectors with the cluster. The route reflectors also peer with other route reflectors in the internetwork. |
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Term
| Describe the origin attribute in BGP? |
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Definition
origin is a well-known mandatory attribute that defines the source of the path information. The 3 types are:
- IGP - indicated by an "i" in the BGP table
- EGP - indicated by an "e" in the BGP table
- Incomplete - indicated by a "?" in the BGP table. Learned from redistribution of the route
The preference goes IGP, EGP, and incomplete |
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Term
| Describe how BGP attributes are categorized |
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Definition
well-known OR optional
| |
---------- -------------
| | | |
mandatory discretionary transitive nontransitive |
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Term
| Describe the use of BGP path attributes |
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Definition
| BGP used path attributes to communicate routing polices. BGP path attributes include next hop, local preference, AS path, origin, multi-exit discriminator (MED), atomic aggregate and aggregator. The most important being the As path |
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Term
| What information is kept in a RIPv1 and 2 forwarding information base? |
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Definition
- ip address
- gateway
- interface
- metric
- timers |
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Term
| What is the timer for EIGRP? |
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Definition
| - EIGRP does not have a periodic update timer. It only sends updates when necessary and sends them only to neighbors using multicast 224.0.0.10 |
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Term
| The composite metric of EIGRP is based on what factors? |
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Definition
| Bandwidth, delay, load, and reliability. MTU is not an attribute for calculating the composite metric. |
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Term
| What are some other used for iBGP? |
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Definition
- Applying policies in the internal AS with the help of BGP path attributes
- QoS policy propagation on BGP (QPPB) - QPPB uses iBGP to spread common QoS parameters from one router to another in the network.
- Multi-protocol BGP peering of MPLS VPN - the multi-protocol version of BGP is used to carry MPLS VPN information between all PE routers within a VPN community. |
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Term
| What are the differences between RIPng and RIPv1 and 2? |
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Definition
| RIPng used UDP port 521, supports IPv6 addresses, and prefixes. RIPng also used IPv6 multicast group FF02::9 |
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Term
| With IS-IS, what is a net? |
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Definition
| A net must be configured on every router. It consists of a domain, area ID, system ID, and elector (sec) |
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Term
| How do designated routers work with IS-IS? |
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Definition
| IS-IS selects DRs on a multiaccess network, but no BDR. The default priority is 64, but can be between 0-127. A priority of 0 means that the router is not eligible to be a DR. In IS-IS, all routers in a multiaccess network establish adjacencies with all others in the subnetwork and IS-IS neighbors become adjacent upon the discovery of one another. |
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Term
| Describe an OSPF totally stub area |
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Definition
| Like a regular stub area, totally stub areas do not flood type 5 LSAs. But they also do not flood network summary LSAs (type 3) or type 4 LSAs. They send just a single LSA for the default route. |
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Term
| What is the default metric when redistributing specific routes? |
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Definition
| There is a default metric of 0 when redistributing routes into Ripv2, IS-IS, and EIGRP |
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Term
| Describe the use of Cisco Group Management Protocol (CGMP) |
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Definition
| Cisco Group Management Protocol (CGMP) is implemented to control multicast traffic at layer 2. Because a layer 2 switch is unaware of layer 3 IGMP messages, it cannot keep multicast packets from being sent to all ports. With CGMP, the LAN switch can speak with the IGMP router to find out the MAC addresses of the hosts that want to receive the multicast packets. |
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Term
| Describe the difference between multicast source and shared trees |
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Definition
With source trees, the tree roots from the source of the multicast group and expands throughout the network in a spanning-tree fashion to the destination hosts
Shared trees create the distribution tree's root somewhere between the network's source and receivers. The root is call the rendezvous point (RP). The tree is created in a spanning-tree fashion with no loops |
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Term
| Describe a OSPF not-so-stubby area |
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Definition
| If an area is configures as a NSSA, the ASBR generates the external LSAs (type 7) into the OSPF system while retaining the characteristics of the stub area to the rest to the AS. The ABR can translate the NSSA external LSAs (type 7) to AS external LSAs (type5) and flood the rest of the internetwork. Or if the ABR is not configured to convert the NSSA external LSAs to typ5 external LSAs, then the NSSA external LSAs remain within the NSSA. |
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Term
| Which version of RIP support authentication, and what types? |
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Definition
| RIPv2 supports authentication, either simple plain-text or MD5 |
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Term
| Describe on-demand routing (ODR) |
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Definition
| ODP is a Cisco proprietary mechanism that eliminates the need for a routing protocol or static routes at a hub router. ODR simplifies the configuration of IP with stub networks in which the hub router dynamically maintain routes to the stub networks. ODR used CDP to communicates between hub and spoke routers, so it must be enabled. The hub router receives the prefix routes from its stub routers |
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Term
| What is the maximum datagram size for a RIPv1 message? |
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Definition
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Term
| Describe the atomic aggregate and aggregator attributes in BGP |
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Definition
| The atomic aggregate attribute informs BGP peers that the local router used a less specific (aggregated) route to a destination without using a more specific route. The atomic aggregate attribute lets the BGP peers know that the BGP router used an aggregated route. A more specific route must be in the advertising router's BGP table before it propagates an aggregated route. When the atomic aggregate attribute is used, the BGP speaker has the option to send the aggregator attribute, which includes the AS number and the IP address of the router that originated the aggregated route |
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Term
| Describe the community attribute in BGP |
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Definition
| The community attribute groups route and applies polices and decisions (accept/prefer) to those routes. The community attribute is an optional transitive attribute. |
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Term
| What are the default timers for IGRP? |
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Definition
- Update - 90 seconds
- Invalid - 270 seconds
- Holddown - 280 seconds
- Flush - 630 seconds |
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Term
| What type of authentication is supported by IS-IS? |
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Definition
- Link authentication - used by routers on a common subnetwork
- Area authentication - all routers in the same area must use the same auth mode and passwords
- Domain authentication - used only by L2 and L1/L2 routers
All 3 are clear-text authentication. |
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Term
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Definition
| BGP is an interdomain routing protocol used to exchange routing information between autonomous systems. The primary function of BGP is to provide and exchange network-reachability information between domains and autonomous systems. BGP is a path vector protocol that is suited for setting routing policies between autonomous systems. It uses TCP port 179 |
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Term
| How many routes can be sored in a single IGRP messages? |
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Definition
| 104 routes per IGRP messages |
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Term
| What are the different administrative distances that EIGRP can have? |
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Definition
- EIGRP summary routes = 5
- EIGRP internal routes = 90
- EIGRP external routes = 170 |
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Term
| Which AS numbers are reserved for private use by ARIN and can't be used by BGP |
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Definition
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Term
| What is included in an OSPFv2 router LSA? |
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Definition
| They include a router's links, interfaces, state of links, and costs. |
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Term
| What does IS-IS use to communicate between router? |
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Definition
| IS-IS uses Layer 2 OSI PDU's to communicate between routers. |
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Term
| What constraints does the OSPF network design have for traffic traveling between areas? |
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Definition
| All traffic from one area must travel through the backbone (area 0) to get to another area |
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Term
| Which Cisco feature can you use instead of local preference to influence the selected path to external BGP routers? |
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Definition
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Term
| Specify the correct order that BGP uses to select a best path |
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Definition
| Weight, local preference, AS path, origin, MED, lowest IP |
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