Contents

Bridging & Switching

RSTP - When a bridge receives a BPDU with the TC bit set from a neighbour, it clears the MAC addresses learnt on all its ports except the one that received the topology change
ERSPAN – Encapsulate SPAN into GRE
802.1q – Protocol type 0x8100 – Tunnelled over ISL
UDLD – Layer 1-2 link detection
802.3z – GE Flow control
PortFast – Access ports
BPDU Guard – If a BPDU is seen on a PortFast port the port is set to ErrorDisable
Uplink Fast – For access switches put alternate port into forwarding when root port goes down
Backbone Fast – For indirect failure when the root bridge is accessible via a different path (Bypasses MaxAge)
Packet flooding – Increase CAM Timeout, reduce ARP timeout or set ARP=CAM timeout
Trunk & Channel negotiation – Desirable Desirable

RIP

Network summarisation in Interfaces

EIGRP

Successor - The best route
Feasible successors - The next best route
Feasible distance – distance
Metric = Bandwidth + Delay
((10,000,000/) + ) x 256

OSPF

Cost = 10,000,000 / Bandwidth (in bps)
auto-cost reference-bandwidth 100
Broadcast & Point to Point 10s 40s
Point to Multipoint & Non-Broadcast 30s 120s

IA Inter Area route
O Intra Area route

Load balancing for Equal cost and type routes
SPF built with self as root, routes are never aged out while hellos are still being received
ASBR – External routes are redistributed as type 5

Defining a Not-So-Stubby Area

router ospf 1
area 1 nssa

No Type 5 LSAs are allowed in area 1. This means no RIP routes are allowed in area 1.
All IGRP routes are redistributed as type 7. This type 7 can only exist within NSSA.
All type 7 LSAs are translated into type 5 LSAs by the NSSA ABR and are leaked into the OSPF domain as type 5 LSAs.

Defining an NSSA Totally Stub Area

router ospf 1
area 1 nssa no-summary

Configure this command on NSSA ABRs only.

No type 3 or 4 summary LSAs are allowed in area 1. This means no inter-area routes are allowed in area 1.

A default route is injected into the NSSA totally stub area as a type 3 summary LSA.

area 1 nssa default-information originate - type 7 default route
Type 7 nssa only p=1 Advertise outside the area p=0 do not advertise

BGP Path Selection

Next hop
Weights (Highest)
Local preference (Highest)
Route that the specified router originated
Shorter AS path
External paths over internal paths
Lowest origin code
Lowest Multi-Exit-Disc Metric
Closest IGP neighbour
Lowest IP address

EBGP sets the next hop address to the IP address of the peer that advertised the prefix
IBGP sets the next hop address to the IP address of the peer that advertised the prefix for routes that originate internally
IBGP passes the next hop unaltered for prefixes that are learned with EBGP

Peer Group – Same update policies
Regular Expressions test for as-path
Next-hop-self sets next hop to my IP to that neighbour

Inbound order:

Route-map
Filter-list
Prefix-list
Distribute-list

Outbound order:

Prefix-list
Distribute-list
Filter-list
Route-map

Well-Known Mandatory

Origin
AS Path
Next Hop

Well-Known Discretionary

Local_perf
Atomic_Aggregate

Common Ports

21 FTP
23 Telnet
25 SMTP
53 DNS
67 DHCP
68 DHCP
69 TFTP
79 Fingers
110 POP3
126 SNMP
137 NetBIOS-NS
161 SNMP
162 SNMP
179 BGP
443 HTTPS
514 SYSLOG

Wireless

Dish / parabolic /grid aerials
Omni
Patch / Panel
Yagi
Sector

T1

Red alarm – Cannot synchronise

SNMP

SNMP-server group [groupname] v3 {auth | noauth | priv}

v3 The most secure of the possible security models.
auth Specifies authentication of a packet without encrypting it.
noauth Specifies no authentication of a packet.
priv Specifies authentication of a packet and then scrambles it.

Inform – Reliable SNMP
Get GetNext Set

Multicast

PIM SM uses RP, Shared Tree, (*,G)
PIM DM uses Source Tree. (S,G)

Auto-RP – PIM Spares-Dense Mode
IGMP snooping (or CGMP), RGMP
DVMRP is Reverse Path Forwarding

Compression

FRF.9 Frame-Relay STAC ppp compression stac
FRF.11-compliant VoFR trunking
FRF.12-compliant end-to-end fragmentation

Header Compression 32K or less
Packet Compression 56K - 2Mb

QOS

The 3 Higher order bits are precedence the next 3 lower order are tos (DHCP)

wrr-queue cos-map queue-id threshold-id cos-1 ... cos-n

CAR – In and Out

Weighted Fair Queuing – Out only

256 Queues (outbound)
Default on links over 2Mb
fair-queue

Custom Queuing – Out only

Custom-queue-list (outbound only)
Round robin
16 Queues of 1500 bytes bandwidth is apportioned by percentage
Queue-list

Priority Queuing – Out only

Priority-group (outbound only)
Strict order
4 Queues High, Medium, Normal, Low
priority-list 1 queue-limit 20 40 60 80

Class-Based Weighted Fair Queuing (CBWFQ) – In and Out

Service-policy input or output
64 Classes
All bells and whistles including RWED
Policy-map

Low Latency Queuing (LLQ)

CBWFQ with a strict priority queue

Crossover Cable

1 Rx+ 3 Tx+
2 Rc- 6 Tx-
3 Tx+ 1 Rc+
6 Tx- 2 Rc-

Security

Smurf – ICMP echo-reply
Standard Access-list – Source address
Extended Access-list – Source & Destination address

Administrative Distance

Connected interface 0
Static route* 1
Enhanced Interior Gateway Routing Protocol (EIGRP) summary route 5
External Border Gateway Protocol (BGP) 20
Internal EIGRP 90
IGRP 100
OSPF 110
Intermediate System-to-Intermediate System (IS-IS) 115
Routing Information Protocol (RIP) 120
Exterior Gateway Protocol (EGP) 140
On Demand Routing (ODR) 160
External EIGRP 170
Internal BGP 200
Unknown** 255

No longer in the exam
As of January 2006

IS-IS

47.0000.0000.    0000    .0000.0000.0000.    00
Domain               Area     System ID                SEL

L2 - Backbone
L1 - Area

IS-IS default metric 10 per link

ISDN

TE1 ISDN Device
TE2 Non ISDN Device (into TA)
NT2
NT1

R-S-T-U