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WAN Final

What is Static NAT? Mapping a private IP address to a public IP address on a one-to-one basis
What is Dynamic NAT? Mapping a private IP address to a public IP address from a pool of public IPs
What is Overloading? (NAT Overload) Dynamic NAT that maps multiple private IP address to a single public IP address by using different ports. Also called PAT.
What is RFC 1918? Private IP address space. 10/8, 172.16/12, 192.168/16
What are the private IP addresses and prefixes?,,
What are some advantages of NAT? Preserve public IPv4 addresses. Adds degree of privacy/security to network. Preserves consistency of internal network design (can change the global IP address without affecting the internal).
Where does a NAT router typically operate? Border of a stub network.
When does NAT take place? Going between an inside and outside interfaces.
What is the difference between inside local and inside global addresses? Inside local = Private source IP of local network, Inside global = Public source IP as seen from the outside network
When would you want to use a static NAT? Servers that must have consistent address that is internet accessible.
If a packet is sent from an inside port to an outside port using port 1444 how does the NAT handle the translation? Sets it to the inside global IP address and will try to keep the same source port of 1444 to mark which computer it came from.
What happens when 2 computers from an inside network send packets to outside networks using the same source port? The router will keep the first one it receives the same port and then use a port starting from the beginning of the appropriate port group 0–511, 512–1,023, or 1,024–65,535
Why is there an issue with using PAT with ICMP packets? ICMP works at layer 3, doesn't have a layer 4 port address to use PAT with.
How does PAT translate an ICMP packet? ICMP has a Query ID field which PAT uses since they don't have a port number.
What are disadvantages with NAT? Network performance, some applications fail, trace issues, complicated tunneling protocols, initiating TCP connections can be interrupted.
Commands to set up a static NAT? ip nat inside source static <localIP> <globalIP>; ip nat inside (on inside interface); ip nat outside (on outside interface)
Command: used to show active NAT translations? show ip nat translations
If you have set up a static NAT use the show ip nat translations command and there are no translations listed what is wrong? The static NAT was not set up properly, static NATs will always show up with the show command, dynamic NATs will not.
Command: used to show information about the total number of active translations? show ip nat statistics; use: clear ip nat statistics, to reset them
How does Dynamic NAT serve IP addresses to devices? Using a pool on a first come first serve basis. If the pool runs out and another device wants an address it will have to wait untill one becomes available.
Command: used to set up a pool for NAT use? ip nat pool NAME <startIP> <endIP> netmask <netmask>; could use prefix-length <prefix> instead of netmask command
Command: used with dynamic NAT to set translation between access-list 1 and pool named NAME ip nat inside source list 1 pool NAME
Using dynamic NAT how long will a translation remain in the table by default? 24 hours, ip nat translation timeout # command will let you change the default
Command: used with PAT (or NAT overload) to set translation between access-list 1 and pool named NAME ip nat inside source list 1 pool NAME overload
Command: used with PAT (or NAT overload) to set translation between access-list 1 and exit interface fa0/1 ip nat inside source list 1 interface fa0/1 overload
Technique which allows an external user to reach a port on a private IPv4 address from the outside? port forwarding
Command: set up port forwarding for local web server on, global ip of ip nat inside source static tcp 80 80
What is the IPv6 version of RFC1918 IPv4 private addresses? ULA (Unique Local Addresses), FC00::/7
How is NAT for IPv6 used? NOT like IPv4 to connect to a private IPv6 address, it is used in IPv6 to transparently provide access between IPv6 only and IPv4 only networks. Called NAT64.
Command: to show NAT debugging information? debug ip nat, in this debug s= source, d= destination
Teleworker advantages: productivity, reduced cost, easier recruit/retention, flexibility
Teleworker disadvantage: Harder to track progress/manage, isolation, distractions, slower connections
Methods used for teleworking? Broadband, IPsec VPN, private WAN technologies
What is DOCSIS? Data-over-Cable Service Interface Specification - international standard developed by CableLabs. Layer 1 + 2 requirements.
Broadband Cable: Which end has the CMTS and which has the CM? CMTS = Cable Modem Termination System on the operator end, CM = Cable modem on the subscriber end
Broadband Cable: What is S-CDMA? Synchronous Code Division Multiple Access
Difference between ADSL and SDSL? ADSL = Asymmetrical, More download than upload. SDSL = Symmetrical, same download and upload
Advantage & Disadvantage of DSL? Non shared medium, length of local loop decreases speeds
Advantage & Disadvantage of Cable? shared medium, distance not a concern
What is microfilter used for in DSL? Seperate the voice channel from the data.
Why is PPP still being used by ISPs? Ability to assign an IP address to link giving customer an IP, CHAP authentication for customers.
In PPPoE what should be done with MTU? Set down to 1492 instead of default 1500 to accommodate PPPoE headers.
Advantages of GRE tunnel? Multiple protocols supported, multicast traffic
What are the configuration steps to setting up a GRE tunnel? Create tunnel, set source IP/interface, set destination IP, set tunnel IP, OPTIONAL set GRE tunnel mode (default)
What are advantages of SSL VPN? Web-based clientless access, does not require pre-installed software.
What are advantages of IPsec VPN? more application support, stronger encryption + authentication, better security
Syslog: Level 0 - 7, which is the most urgent? 0 = emergency and most urgent, 7 = debug and rarely used.
Syslog: %LINK-3-UPDOWN ... what does this mean? Facility = LINK, Severity = 3, MNEMONIC = UPDOWN
Verify: Logging info show logging
Configure: logging of level 4 and below from interface g0/0 to syslog server at logging; logging trap 4; logging source-interface g0/0
Command: send logging messages to a telnet session? terminal monitor
SNMP: where do traps, gets, and sets get configured? trap on the agent sends messages to manager, gets and sets on manager to poll the agents
SNMP: where does information get stored? MIB - management information base
SNMP: difference between v1, v2, and v3? v1 = clear text, community string, v2 = community string, v3 = encryption & authentication
SNMP: verify command show snmp
What 7 fields did original netflow monitor? source+dest IP+port, layer 3 protocol, interface, type of service ToS marking (QoS)
NetFlow: display stats summary show ip cache flow
NetFlow: display interface configs (egress / ingress) show ip flow interfaces
NetFlow: display export config show ip flow export
Created by: Datheral