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38 Cards in this Set

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To clear dynamically learned MACs from a switches MAC address table. This can help determine if a previously learned MAC is relearned.
SW1# clear mac address-table dynamic
Displays MAC addresses learned by a switch along with each associated port and VLAN of the MAC.
SW1# show mac address-table dynamic
To show to which VLANs the ports of the switch belong.
SW1# show vlan
To see info about encapsulation, mode, native VLAN, which ports are configured as trunks and which VLANS are permitted (allowed) on the trunk ports.
SW1# show interfaces trunk
To display summary info for the ports on a switch, including VLAN and trunk configuration information. Shows pre-configured settings and actual settings.
SW1# show interfaces switchport
To see a list of switches that would be transited for traffic traveling from a specified src MAC to a specified dst MAC. Uses CDP info to produce the list.
SW1# traceroute mac [src MAC] [dst MAC]
To see info about the STP state of the switch. Shows the Root ID, Bridge ID, timer values and the different roles of the switches interfaces.
SW1# show spanning-tree vlan [vlan-id]
To show information contained in BPDUs, in addition to the number of BPDUs sent and received.
SW1# show spanning-tree interface [type] [mod/num] detail
To display the routers Layer 3 forwarding information (FIB), which is basically a the routing table formatted into a ordered list with the most specific route first. Keeps the layer 3 next hop address for each entry. Has columns for prefix, next hop and interface.
R1# show ip cef [prefix-ip] [prefix mask] [longer-prefixes] [detail]
Verifies a valid adjacency exists for a connected host. Consists of the MACs of nodes that can be reached in a single L2 hop. The L2 entry for every next hop entry. Adjacencies are kept for each next hop router and each host that is connected directly to the local switch.
R1# show adjacency [detail]
To show the total number of adjacencies known on each physical or VLAN interface.
R1# show adjacency summary
To set up a HSRP group with a VIP.
R1(config-if)# standby [group no.] [vip]
To set the HSRP priority. Default is 100. Highest priority wins.
R1(config-if)# standby [group no.] priority [priority]
To set the HSRP interface as pre-emept, so if it has a higher priority when it comes up will send a coup message and take over as the active router.
R1(config-if)# standby [group no.] preempt
To show a routers HSRP interface, group number, priority, state, VIP and the standby IP in a table format.
R1# show standby brief
To see detailed HSRP configuration information applied to a specified interface in a specified group (optional).
R1# show standby [type] [mod/num] [group no.]
To show HSRP state changes and information about sent and received HSRP packets.
R1# debug standby
To see a summary view of a routers VRRP configuration. Same principle as HSRP, but pre-empts by default and the IP serviced by the VRRP group doesn't have to be a VIP, can be the IP of a physical interface on the Master virtual router.
R1# show vrrp brief
To see a summary view of a routers GLBP configuration. It load balances traffic over a selection of AVFs (decided by weighting) by replying with different MACs to clients ARP requests.
R1# show GLBP brief
To check port statistics so you can see whether packets are being dropped (could be due to congestion or bad cabling). Displays the number of inbound and outbound frames seen on the specified port.
R1# show interfaces [type] [mod/num] counters
To see the errors that occurred on a port. May have Xmit-err or Rcv-err if the ports transmit or receive buffer overflows.
R1# show interfaces [type] [mod/num] counters errors
To display the CPU utilization levels. The first % is the CPU load, and the second % the cpu load used for interrupt processing. A typical cpu load used for interrupt processing for a switch is 5 to 10%, since CPU isn't actively involved in forwarding packets since is handled by TCAM. On a router it is normally higher since cpu handles the forwarding.
SW1# show processes cpu
To enable Automatic medium-dependant interface xrossover (auto-MDIX) feature on an interface to automatically detect and adjust to the connected cable type (that is, either straight-through or xross-over).
R1(config)# mdix auto
To display the amount of TCAM memory allocated and used for inbound access lists.
SW1# show tcam inacl [tcam no.] statistics
What are 2 of the big differences between switches and routers?
Routers use a wider selection of interface types and their IOS types support much more features than switches.
What are the 2 primary components of forwarding hardware and how can they affect performance?
Forwarding logic and the back plane. A back plane is rarely the cause of a switch performance issue since most switches have high capacity back planes. However a multilayer switches forwarding logic can impact performance since it is compiled into TCAM which provides extremely fast forwarding decisions. If TCAM is unavailable to forward traffic for some reason, the CPU has to forward it. The CPU has a limited forwarding capacity.
Which switch/router operations can be categorized as control plane?
Routing protocols and ARP. A switches CPU and memory reside in a control pane, and it is responsible for running the switches o/s. The control plane doesn't directly participate in frame forwarding, however the forwarding logic contained in the forwarding h/w comes from the control plane.
What router operations can be categorized as data plane?
The actual forwarding of data is handled at the data plane, since it physically interconnects a switches ports. A router uses CEF to efficiently forward the data by creating a FIB and Adjacency table (from info collected from control plane) that reside in the Data Plane.
What switch operations can be categorized as data plane?
L3 switches also leverage CEF to efficiently route packets, but yet some switches take the info contained in CEFs FIB and Adjacency table to compile the TCAM. This special memory type uses a mathematical algorithm to very quickly lookup forwarding info.
When is a routed port considered to be in a down state?
If it is not operational at both L1 and L2. A routed port doesn't run switch protocols such as STP or DTP.
When is a Switched Virtual Interface (SVI) considered to be in a down state?
When none of the ports in the corresponding VLAN are active.
What are the STP Default Port costs?
10MBPS=100, 100MBPS=19, 1GBPS=4, 10GBPS=2
What's the format of a virtual MAC for HSRP?
xxxx.xx07.acxx, with first 6 being the vendors MAC code, middle 4 being the well known HSRP code, and last 2 being the HSRP group number in hexadecimal format.
What are the 2 biggest indicators of a duplex mismatch?
A high Rcv-err counter on the full-duplex end of the mismatch, while a Late-col counter is common on he half-duplex connection. Carri-Sen is also an indication of half-duplex since the Carrier Sense procedure is part of the CSMA/CD operation used on half-duplex connections.
What would normally cause processor utilization spikes?
CPU processing routing updates or issuing a debug cmd or other processor intensive cmds.
What are some of the collision errors you may see from the counter errors cmd?
Single-col=Single collision occurs before frame successfully sent, Multi-col=More than 1 collisions occurs before frame successfully sent, late-col=Collision not detected until well after frame is forwarded, Excess-col=Frame experiences 16 successive collisions, after which a frame is dropped.
What are runt and giant errors that you may see from the counter errors cmd?
A runt is a frame less than 64bytes in size and has a bad CRC, whilst a giant is a frame greater than 1518bytes that has a bad FCS.
What's the name of the process of the TCAM sending packets to the CPU, and name some of the reasons it does so?
Punting. For routing protocols and other control plane protocols such as STP, someone connecting remotely (e.g. telnet), packets using a feature not supported in h/w (e.g. GRE tunnel) or if the TCAM has reached its capacity.