Term
| What forwarding decision does a switch (bridge) make on receiving a unicast frame? |
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Definition
If the source and destination hosts are associated with the same port on the switch, frame is dropped.
If the destination is in the switch CAM table, then forward only to the associated port.
If destination is not known, broadcast (flood) on all ports except the originating one. |
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Term
In STP, how is the root bridge elected?
What are its characteristics? |
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Definition
Switch with lowest Bridge ID is root,
where Bridge ID = [ Admin Priority | MAC ]
All ports are in forwarding state. |
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Term
What are the port states in STP?
What are their characteristics? |
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Definition
1. Blocking - listens but does not send BPDUs
2. Listening - blocked port begins to send BPDUs
3. Learning - when switch is still populating the MAC address table; no frames are forwarded
4. Forwarding - normal operation for a non-blocked port.
Also:
Disabled - port does not participate in STP
Portfast - Immediately brings access/trunk link from blocked to forwarding state. Allow hosts to connect without waiting for STP.
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Term
What are the characteristics and purpose of:
BPDU Guard
BPDU Filter
Root Guard
Loop Guard |
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Definition
BPDU Guard - Prevents devices on portfast ports from hijacking as STP root (DoS). Places ports in err-disabled state if detects BPDUs.
BPDU Filter - Prevents sending BPDUs to portfast ports (reconnaisance attack).
Root Guard - Enforces root; puts desginated port in root-inconsistent state if superior BPDU is seen.
Loop Guard - Places root/alt ports in inconsistent state if no BPDU traffic seen. |
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Term
| What are the steps to establishing a TCP connection? |
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Definition
Three-way handshake:
1. A --> B : SYN with seq(A)
2. A <-- B : SYN with seq(B), ACK with seq(A+1)
3. A --> B : ACK with seq(B+1) |
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Term
| What are the steps to tear down a TCP connection? |
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Definition
1. A --> B : FIN_ACK [seq(A), ack(B+1)]
2. B --> A : ACK [seq(B),ack(A+1)]
3. ...waits...
4. B --> A : FIN_ACK [seq(B),ack(A+1)]
5. A --> B : ACK [seq(A), (B+1)] |
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Term
Identify the port & transport type:
FTP
DHCP
DNS
HTTP/HTTPS
NTP
SMTP
Syslog
TFTP |
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Definition
FTP : TCP 20, 21
SMTP : TCP 25
DNS : TCP / UDP 53
DHCP : UDP 67, 68
TFTP : UDP 69
HTTP/HTTPS : TCP 80/443
NTP : UDP 123
Syslog: TCP/UDP 124
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Term
What are the characteristics of the following TCP services:
ARP
RARP
Inverse ARP
Gratuitous ARP |
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Definition
ARP - MAC address resolution when IP is known
Reverse ARP - requests IP for specific MAC during bootup; replaced by DHCP
Inverse ARP - resolve the remote side DLCI in frame relay
Gratuitous ARP - broadcast updates of new MAC address/MAC address after change of device |
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Term
What criteria is used to determine which route is placed in the routing table given multiple routes to the same destination? |
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Definition
1. If learned from different routing protocols: use route with lowest administrative distance
2. If learned from same routing protocol: use route with lowest metric/cost
3. If all else above the same, use route with the longest prefix match |
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Term
What are the administrative distances for the following routing protocols and which is preferred?
Connected
EIGRP (internal/external)
IGRP
OSPF
RIP
Static (not configured) |
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Definition
Lowest AD is preferred
Connected - 0
Static (default) - 1
EIGRP (internal) - 90
IGRP = 100
OSPF - 110
RIP - 120
EIGRP (external) - 170 |
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Term
| What are the characteristics of path vector routing protocol? |
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Definition
| Routing information exchange also propagates on the path of autonomous systems via which the route was learned from. |
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Term
| What are the differences between RIP and RIPv2? |
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Definition
RIP: classful, broadcast
RIPv2: classless, multicast to 224.0.0.9, supports authentication for sessions and equal-cost load balancing |
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Term
What are the characteristics of RIP
(name, type, transport, security) |
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Definition
Routing Information Protocol
classful, distance vector routing protocol
UDP port 520
no security |
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Term
What are the characteristics of OSPF?
(type, algorithm, dstIP, security) |
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Definition
Link state routing protocol.
Calculates best path using Shortest Path First (SPF) or Djikstra's algorithm
Updates multicast to AllSPFRouters=224.0.0.5 or ALLDRouters=224.0.0.6
Auth, 3 modes: null (default), plain text, MD5 |
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Term
| What is the area id for the "backbone" area for OSPF and how does it relate to other areas? |
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Definition
Area 0
All other areas must be connected to it. |
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Term
What is the purpose of a designated router in an OSPF network?
What is the process for electing a desginated router and backup DR? |
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Definition
Conserve bandwidth by having all other routers (more than one) communicate with the DR instead of each other in full mesh
Router with highest priority on the segment becomes DR (and second highest becomes BDR).
If tie, router with the highest router ID becomes DR |
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Term
What are the characteristics of EIGRP?
(type, algorithm, security) |
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Definition
Classless, Hybrid protocol (between distance vector and link state)
Cisco proprietary
Uses DUAL Algorithm for faster convergence
Authentication - same as RIPv2 (key chain, md5) |
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Term
What are the characteristics of BGP?
(transport, routing protocol type, routing method, security) |
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Definition
TCP port 179
Path vector protocol.
Maintains table of info about all probable paths to destination. Best path is imported into routing table
MD5 authentication available. |
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Term
What are the characteristics/purpose of BGP:
Route Reflectors
Confederations? |
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Definition
Both are used to work around the requirement for full mesh in iBGP topology, improving scalability
Route Reflectors - Multiple BGP routers ("clients") peer with one RR server (similar to OSPF DR)
Confederation - subdivide AS into multiple internal sub-AS; still advertises single AS to external peers. |
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Term
What are the characteristics of IGRP?
(name, type, security) |
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Definition
Interior Gateway Routing Protocol
classful, distance vector routing protocol
no security/auth |
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Term
What are the characteristics of multicast addresses?
What are the special addresses used to send messages/updates to subsets of hosts. |
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Definition
Class D addresses
224.0.0.0 to 239.255.255.255
all hosts: 224.0.0.1
all multicast routers on subnet: 224.0.0.2 |
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Term
What are is the:
first octet range
high order bits
(default subnet mask)
for:
Class A, B, C, D, E IP addresses? |
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Definition
class / first octet range / high order bits / (mask)
A: 1-126 (127 bcst) / 0 / 255.0.0.0
B: 128-190 (191 bcst) / 10 / 255.255.0.0
C: 192-222 (223 bcst) / 110 / 255.255.255.0
D: 224-239 / 1110
E: 240-255 / 1111 |
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Term
| What IP ranges are assigned to private address spaces for class A, B, C IP? What standard defines this? |
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Definition
Class A: 10.0.0.0 / 8
Class B: 172.[16-31].0.0 (172.16.0.0 /10)
Class C: 192.168.0.0 / 16
RFC 1918 |
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Term
| What are the commands used to configure dynamic NAT using a pool as the outside range and an ACL for the inside source? |
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Definition
Global:
ip nat pool [name] [1stIP] [lastIP] netmask [mask]
or
ip nat pool [name] [1stIP] [lastIP] prefix-length [#]
ip nat inside source list [acl#] pool [name]
Interface:
ip nat [inside|outside] |
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Term
| What are the commands to enable PAT? |
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Definition
Global:
ip nat inside source [...] interface [intfc] overload
Interface:
ip nat inside/outside |
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Term
| What is the process to change the MD5 auth keys for OSPF authentication? |
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Definition
Multiple keys (Key Identifier) can be associated with same interface.
New key set to start on all devices before the old key lifetime expires. During overlap time, devices will process messages using either key.
Thus smooth transition is possible. |
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Term
What do the following NAT related RFC's cover?
1631
2663
3235 |
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Definition
RFC 1631 - Basics of NAT and routing
RFC 2663 - Definitions of the various type of NAT (NAPT, PAT, etc); mechanisms and effects on other protocols (tunnels, DNS, FTP, etc)
RFC 3235 - Recommendations for new protocols to take into account regarding NAT; Limitations of NAT and failures when working with other protocols |
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