Use the ip default-network command to configure the gateway of last resort. use the ip default-gateway command when routing is disabled.
The hierarchical design model consists of a core, distribution, and access layers. The distribution layer implements access lists, distribution lists, route summarization, VLAN routing, security policy, and address aggregation.
Distance vector routing protocols periodically send a copy of the full routing table to neighboring routers.
The preferred reading for reliability is 100 percent or 255/255. The preferred reading for load is the nearest 0 percent or 1/255.
OSPF requires a two-layer topology with all areas connecting to the backbone. With link-state routing protocols, the status of each router in the network is propagated to all other routers in the network, and each router calculates the best routes in the network.
The correct format is ip route 0.0.0.0 0.0.0.0 serial 0 to configure the default route out of serial int.
Split horizon with poison reverse sends a route with an infinite metric out the interface from which it learned the route.
The core layer of the hierarchical design model uses high-speed connections.
The least significant number of the configuration register (ox2101) determines which image is loaded. If set to 0x1 (0001 binary), the router boots the ROM image.
The switch show port status command in switch provides a summary table of interfaces with port number, VLAN, and Status information. The show ip interface brief command in router provides same output a summary table of interfaces with interface name and number, IP address, and status information.
When accessing the router through Telnet, the terminal monitor command needs to be configured to view debug output.
The configuration register setting can be verified with the show hardware or show version command.
The password configured with the enable secret command overrides the password configured with the enable password command.
The o/r 0x2142 command is usually configured during a password recovery
procedure. It modifies the configure register by telling the router to ignore the
configuration in NVRAM.
The system bootstrap initializes the CPU and starts the bootloader.
The copy tftp running-config command configures the router from a network TFTP server.
The snmp community ccie rw command allows the network management server to write changes on the router.
If the login command is configured for all vtys but not the password command, the router prompts with password not set and disconnects the Telnet session.
The show process cpu command shows the five second, one minute, and five minute CPU use time for each process on the router.
A router is in ROM monitor mode if it has one of the following two prompts: > rommon >
Reboot, break, set 0x2142, reboot, copy password, disable ignore NVRAM, reboot is a correct process for password recovery.
If you use the login command, but the password is not set for vty lines, Telnet access is not granted. The router returns a password not set message and disconnects the Telnet session. If you do not use the login command, users are granted access without prompting for passwords. If you access the router through a virtual terminal, such as Telnet, you need to enter the terminal monitor command to have debug output show on your screen. This command is not necessary if you access the router from the console.
Ethernet is canonical; it expects the least significant bit first to read off the wire. Token Ring is noncanonical; it expects the most significant bit first.
The IEEE 802.3 SNAP frame contains an Ethernet type field in the SNAP field. Transparent bridges create a table that associates learned MAC address with its ports. IEEE 802.1q identifies the VLAN by using an internal tag. ISL uses an external tag.
The VTP client participates in VTP by maintaining a list of VLANs but does not store the information in NVRAM, nor can it add, delete, or rename VLANs.
The bridge identifier (BID) is used in the Spanning-Tree Protocol. The BID is 8 bytes long and contains a bridge priority (2 bytes) along with one of the bridge’s MAC addresses (6 bytes).
Bridge virtual interfaces configure integrated routing and bridging (IRB).
VTP servers maintain a full list of VLANs, adds and deletes VLANs, and stores VLAN information in NVRAM.
Transparent bridges learn MAC addresses, filter frames with destination MAC addresses located on the same incoming port, and forward frames to the port associated with the destination MAC address.
Spanning-Tree Protocol enables blocked interfaces if the primary link or bridge fails.
The path cost is the addition of segment costs to reach the root bridge.
With CDP, the neighbor’s device name, management IP address, platform type, and OS version can be gathered.
IEEE 802.1x specifies a port-based authentication mechanism that uses EAP and RADIUS.
The Basic Service Set mode uses one Access Point for clients to access the wired LAN.
BSS is also referred to as Infrastructure mode.
The LAN Emulation Configuration Server (LECS) is contacted first by joining LECs. The LECS provides the ATM address of the LES to the client.
LE-ARP translates MAC addresses to ATM addresses.
X.25 uses LAPB, a variant of HDLC, for Layer-2 framing.
Discard Eligible bit is set on frames exceeding the Committed Information Rate (CIR), which is the contracted traffic rate by Frame Relay network switches or is set by the Frame Relay DTE (router) on relatively low priority frames. Frames with the DE bit set are discarded in a congested network before frames without the DE bit set.
NT1 is a physical layer device that connects the 4-wire BRI from ISDN equipment to the 2-wire phone line provided by the telephone company.
The BECN bit is set in frames traveling from the destination to the source when congestion occurs in the Frame Relay network on the path from the source to the destination. A BECN attempts to throttle the rate of traffic being sent by the source DTE.
Routers on Frame Relay networks learn local DLCIs by using LMI. Then, they learn the remote IP address associated with the local DLCI through the inverse-arp process.
There are 10 bits in a Frame Relay DLCI without extended addressing.
PPP supports PAP and CHAP authentication. PAP uses clear text passwords; CHAP uses encrypted passwords.
ISDN D channels use the LAPD framing standard. The ATM header is 5 bytes, the payload is 48 bytes, and the entire cell is 53 bytes. ATM payload cells are identified by the VPI/VCI pair.
Frame-relay supports flow control. ABR provides flow control mechanisms to alter source rate.
BECN bits are sent to the source end station in an attempt to throttle the sending traffic rate. If traffic shaping is enabled, the router uses these BECN bits to control the flow of frames into the network.
Frame Relay has fewer error checking features than X.25; therefore, it is not designed to run over bad cable systems. Both X.25 and Frame Relay are connection-oriented.
Frame Relay adds less overhead; therefore, it is available at greater speeds.
Frame Relay networks drop frames when there is congestion in the network and do not retransmit them. The sending host must retransmit any dropped frames. Circuit-switched networks use synchronization, where synchronous circuits are dependent on having the same clock so that the receiving side knows exactly when
each frame bit is received.
Each B channel has the bandwidth capacity of 64 kbps.
Telnet uses IP protocol 6, which is TCP. TCP uses port 23 for Telnet.
The IP protocol layer at the destination host is responsible for reassembling any IP fragments before sending the packet up to TCP.
TCP waits for data to accumulate before forming a segment. The PSH pointer indicates to promptly send the data.
The PING application uses the Internet Control Message Protocol (ICMP) echo type.
The Bootstrap protocol(BOOTP) and the Dynamic Host Configuration Protocol (DHCP) are methods to provide an IP address, mask, and a default gateway to a host.
The real IP address of a device in the internal network is translated to a globally unique address, which is the Inside Local Address.
The ip helper-address supports BOOTP, DHCP, NETBIOS, TFTP, DNS, TACACS,
Time service, and IEN-116 name service by default.
Four segments close a TCP connection.
The Internet header length (IHL) is measured in 32-bit words.
proxy-arp is configured on an interface.
The router with the highest HSRP priority becomes the active router. The default HSRP priority is 100.
TCP connections are established with a three-way handshake.
There are 3 bits in the precedence bits field. The IP checksum is computed for the IP header only.
IP provides best-effort delivery. If a fragment is lost, the upper layer is responsible for detecting missing data and for requesting a retransmission.
The checksum is performed on the TCP header, data, and psuedo-header.
The sequence number indicates the first byte in the segment.
standby 1 track serial 0 is used if you want the active HSRP router to resign if a tracked serial interface 0 goes down
Outside global addresses are not translated; therefore, the address remains the same after the packet passes through the NAT router.
If EIGRP and IGRP are configured with the same AS number in a router, they automatically redistribute routes without having to use the redistribution command.
There can be up to 25 routes in a RIP update packet.
By default, EIGRP uses bandwidth and delay in its composite metric.
By default, EIGRP summarizes routes at network boundaries.
EIGRP places a route into active state when performing a recomputation for the
route.
If a route is removed, no new updates for the route are accepted until the holddown timer expires. The hold-down timer for RIP is 180 and for IGRP is 280.
EIGRP scales the metric by 256.
By default, EIGRP loads balance using equal-cost paths. EIGRP does unequal load balancing when you use the variance command.
An OSPF backbone router always has one or more interfaces connected to the Area 0. An ASBR can have one or more interfaces connected to the backbone, but it isn’t a requirement.
IS-IS supports cleartext password authentication only. In Cisco routers, all IS-IS interfaces have a default metric of 10.
All areas are required to connect to the OSPF backbone. If an area does not have physical connectivity to the backbone, but it does connect to another area that connects to the backbone, a virtual link can provide the required area to the backbone connection.
External routes advertised in a not-so-stubby area are flooded within the area with Type-7 LSAs.
Type 3 LSAs are summary LSAs. Type 4 LSAs announce reachability to the ASBR.
Type 5 LSAs announce AS external routes. Type 7 LSAs announce external routes within an NSSA.
Costs are associated with interfaces. The ip ospf cost command changes the default cost of an interface.
ASBRs set the P-bit in Type 7 LSAs. An ABR receiving the LSA translates the Type 7 LSA to a Type 5 LSA if the P-bit is set to 1.
The attached (ATT) bit is set by a L1/L2 IS to indicate that it is attached to an L2area and is, therefore, available to forward traffic outside of the L1 area.
The DR forms adjacencies with all routers in a multiaccess network.
IS-IS multiaccess networks have designated ISs only, no backup designated IS
(BDIS) exists.
OSPF does equal-cost, multipath load balancing.
OSPF does not do unequal-cost, multipath load balancing. If two paths exist to the
same destination, OSPF chooses the path with the lowest cost.
IS-IS does not run over IP.
Type 3 LSAs are Summary LSAs and are produced by ABRs. They are flooded into
areas to advertise destinations outside the area.
If two paths exist to a single destination, the L1 path takes precedence, regardless
the cost. The E-bit specifies whether an area supports external routes. If the area does not
support the flooding of external routes, the area is a stub area and the E-bit must be
cleared in Hello packets on all interfaces in the area. If the area does support external
routes, the area is not a stub area and the E-bit must be set.
Multi-Exit Discriminator (MED) is used when an AS has multiple connections to
another AS. It is an attempt by an AS to influence the selected route a neighboring
AS should select.
The Weight attribute selects the best outbound route, it is not advertised to peers, and
it is locally significant. The highest Weight is selected.
BGP synchronization requires that BGP speakers in a transit AS not advertise routes
until all routers within that AS have learned about the route through an IGP.
BGP communities apply a common policy or properties to a group of destinations.
The selected route is marked with the > symbol.
External BGP routes have an administrative distance of 20. Internal BGP routes
have an administrative distance of 200.
Route dampening suppresses flapping BGP routes.
Classless Interdomain routing (CIDR) was first implemented in BGPv4.
BGP Multihop is configured to peer with an external BGP neighbor that is not in a local subnet.
BGP peer groups apply a common set of policies to a group of BGP neighbors.
The lowest BGP MED is selected.
The highest local preference is selected. The default local preference is 100.
One or more route reflectors are allowed in a cluster.
NLRI is Network Layer Reachability Information, which are destination IP networks.
Hosts use Internet Group Management Protocol (IGMP) to join a multicast group.
IGMP operates between the host and the local router.
The IANA has reserved addresses in the range from 224.0.0.0 through 224.0.0.255
that network protocols use on a local network segment. The address 224.0.0.1 means
“all systems on this subnet,” 224.0.0.2 means “all routers on this subnet,” and
224.0.0.5 is for OSPF routers.
On Cisco routers, OSPF external routes have an administrative distance of 110. The
distance of OSPF external routes can be changed by using the distance external
command.
Distribute lists filter the contents, inbound or outbound, of routing updates.
Protocol Independent Multicast is a multicast routing protocol. The two flavors of
PIM are sparse mode and dense mode.
The network mask pair 0.0.0.0 255.255.255.255 signifies any network.
The distance external command can assign an administrative distance, which is
different than the default (110), to OSPF external routes.
The RIP route is entered in the routing table because the administrative distance of
RIP is 120 and the administrative distance of IBGP is 200.
The rendezvous point (RP). The RP is charged with the task to gather the
information of senders and make the information available to other PIM routers.
Cisco Group Management Protocol (CGMP) and IGMP Snooping are both methods
to control multicast traffic in a switched LAN environment.
Policy-based routing can change the next-hop address based on the source IP
address of the packet.
Auto-RP and PIM Bootstrap Router (BSR) are methods for PIM networks to
configure the RP automatically for multicast groups.
Priority queuing (PQ) always empties the high queue before servicing the lower
priority queues.
The Resource Reservation Protocol (RSVP) is a signaling protocol that enables hosts
to obtain special qualities of service for data traffic.
Weighted random early detection (WRED) drops packets to prevent congestion.
WRED expects TCP to reduce its window size as packets are dropped and, therefore,
to transmit fewer packets.
Generic Traffic Shaping (GTS) is configured with the traffic-shape command. This
command controls the traffic flow on an interface.
EIGRP and IGRP can load balance over unequal-cost paths. Cisco’s implementation
of OSPF, ISIS, and RIP can load balance over equal-cost paths.
By default, EIGRP uses four paths for load balancing to a destination. EIGRP can
be configured to load balance up to six paths. The paths do not need to have equal
costs.
Implementation FRF.9 of the Frame Relay Forum defines compression on Frame
Relay networks. FRF.5 is the Frame Relay/ATM Network Interworking
Implementation. FRF.11 is the Voice over Frame Relay Implementation Agreement.
FRF.12 is the Frame Relay Fragmentation Agreement.
Multi-Protocol Label Switching inserts a 32-bit field, which includes a 20-bit tag, between the
Layer-2 header and the Layer-3 header.
Stacker is a Cisco enhanced version of the Lempel-Ziv (LZS) compression
algorithm.
Custom queuing (CQ) can configure up to 16 queues to prioritize traffic.
Only Committed Access Rate (CAR) uses the rate-limit command.
OSPF can be configured to use up to six equal-cost paths.
EIGRP can be configured to use up to six equal-cost paths.
Custom queuing is configured by creating queues with the queue-list protocol command, assigning byte counts to the queues with the queue-list queue byte-count command, and then configuring the interface with the custom-queue-list command.
Priority queuing uses four queues: high, medium, normal, and low.
DSCP uses 6 bits, which produce 64 values for packet classification.
TACACS authentication protocol uses TCP.
The triple DES (3DES) key is 3 × 56 bits = 168 bits.
Real-Time Transport Protocol (RTP) operates in the transport layer of the OSI
model.
The Q.931 standard defines the procedures responsible for call setup and signaling.
Erlangs is the unit that describes the number of calls in one hour.
NLSP and IPX EIGRP routing protocols reduce IPX broadcast traffic.
The 80-bit IPX address consists of the 32-bit network number plus a 48-bit MAC address.
RADIUS uses UDP port 1812 or UDP 1645 and UDP 1646. TACACS uses TCP.
The G.711 codec produces a 64 kbps bit rate.
The Signaling Control Point (SCP) is a database for special call processing and routing.
Authorization determines which resources are accessed. Authentication determines who is the user. Accounting keeps track of what resources were accessed, by whom and when.
TACACS+ separates AAA functions into separate modules. RADIUS combines authentication and authorization.
The PIX Firewall uses the Adaptive Security Algorithm (ASA) for stateful, connection-oriented security.
The IPX address is 80 bits in length, consisting of a 32-bit network part and a 48-bit host part.
NetWare Link Services Protocol (NLSP) is a link-state protocol that is based on IS-IS.
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