| what is DHCP ? | Dynamic Host-Configuration Protocol (DHCP)
- A Dynamic/Automatic method to assign IP Addresses .
- Not only IP Addresses:
- Subnet Masks
- Gateways
- DNS!!
- Assignment will be for a specific amount of time (default 24 hrs.) |
| What is DNS ? | - Domain Name Server: resolve a URL to an IP Address and vice-versa .
- also, there is a reverse DNS (for that vice-versa thing) |
| which method and port does DNS use ? | UDP port 53 . |
| assignment time of DHCP ? | - after 50% of assignment time begins, some checks will happen for each
Client, and again after 87.5% of the assignment time, another check
Will take place. |
| dhcp process order? | .. |
| what if the first router (Gateway) wasn’t a DHCP Server!!?? | - there will be a “Helper-Address” .
- known as “DHCP Relay” .
- help redirecting the broadcast message from the first Gateway to the
Correct DHCP Server . |
| what is (FHRP) ? | First Hop Redundancy Protocol .
what if the gateway went down!!!!!!!!
- a redundant gateway must be there . |
| What protocols will FHRP use ? | - Hot-Standby Redundancy Protocol
(HSRP)(cisco only ).
- 2 Gateways
- No Load-Balancing
- Virtual-Router Redundancy Protocol
(VRRP) (same of above but open standard)
- Gateway Load-Balancing Protocol
(GLBP)( cisco only) - 4 Gateways , Load balancing . |
| what is (NAT) ? | Network Address Translation
- Private IP Addresses don’t carry Internet!
- Public IP Addresses can’t be assigned to private devices!
- Then!!!, NAT will translate Private to Public and vice-versa
*NAT is done ONLY ONLY by Routers, no Switches, no MLS’s |
| two ways to apply NAT ? | - it can be:
Static: one-one translating
Dynamic: Group-Group Translating |
| what is PAT ? | It provides wider options as one address can be used for more than one device by specifying the IP address with the port number .
- PAT (Port Address Translation) .
- also called NAPT, or NAT-Overload
- PAT will do a one-65535 Translation!!! |
| what is NTP ? | - we have to stay synchronized
- give a precise information, with real timing and date
- either by setting an inner clock manually
- or asking someone to inform us about timing.
- each network device can either be a Server or a Client |
| which method and port does NTP use ? | uses UDP = 123 |
| what Stratum (NTP server ) is needed ? | - how preferred and accurate this source is
starts from 0 – 15.
the closest, the better.
- by default: a cisco router = 8 |
| which command NTP use to tell " I am NTP srver " ? | ntp master |
| which command NTP use to tells " That is NTP server " ? | ntp server <some IP > |
| what is SNMP ? | Simple Network Management Protocol (SNMP) .
- Monitor Networks from a single point of view
- Server/Agent Relationship |
| which method and port does SNMP use ? | - uses UDP 161/162 |
| server/agent in SNMP ? | - the server is thee requester (and recorder)
- at the agent side:
- MIB Object (The Factory)
- Agent (The Messenger) |
| - SNMP versions ? | - v1: obsolete [dead]
- v2c: enhanced [dead]
- v3: supports Authentication & Encryption [alive]
ptrg an example of GUI program using SNMP |
| what is Syslog ? | System Loggings (Syslog)
- stay aware of “everything”
- know all what’s happening behind the scenes (or even in front of)
- starts from the obvious informations up to “Emergencys” |
| server/client in Syslog ? | - Server can be a Normal Server that collects all the loggings
- Server can use the “Syslog” or “Splunk” Software
- client is the networking device that generates logs |
| what is the message '0' (syslog) ? | 0 = Emergency |
| what is the message '1' (syslog) ? | 1 = Alert |
| what is the message '2' (syslog) ? | 2 = Critical |
| what is the message '3' (syslog) ? | 3 = Error |
| what is the message '4' (syslog) ? | 4 = Warning |
| what is the message '5' (syslog) ? | 5 = Notification |
| what is the message '6' (syslog) ? | 6 = Information |
| what is the message '7' (syslog) ? | 7 = Debug |
| what is QoS ? | Quality of Service (QoS)
- if traffic was more than bandwidth!
- if congestion WILL happen,
can some traffic be more preferred than another!?
- Generally, UDP will be preferred over TCP (TCP will automatically do
A retransmission). |
| QoS will prefer based on Variety of Factors, some are ? | ll |
| what is classification and Marking, Queueing ? (Qof) | - Classification & Marking:
classifying the traffic according to its importance
(Very High, High, Med, Low)
- Queueing:
- giving a specific priority to every type of packet
(giving the priority of "very high" to the "UDP" traffic)
- dividing the Transmission capacity with respect to the priority
(giving 40% to the very high, 20% to the high, etc.) |
| what is policing and Shaping ? (QoS) | - Policing & Shaping:
- Policing is counting the traffic before transmitting it, and limiting it
(limit the FTP traffic to be transmitted at maximum of only
2Mbps)
*counting the desired traffic, and dropping all that exceeds
- Shaping limits the Queued traffic to a certain amount of traffic, and
what EXCEEDS, wait at the queue . |
| what is SSH ? | Secure Shell (SSH)
- A secured and trusted method to log in a device remotely.
- encrypt the transmitted information
- uses the server/client relationship
- a replacement for Telnet
- needs an application for (Microsoft Windows Users) . |
| what port and method does SSH use ? | what uses tcp port 22 |
| what is FTP ? | File Transfer Protocol (FTP)
- can devices transfer data between them?
- data like Files, Software Images, Configs saved as Texts |
| what port and method does SSH use ? | - FTP uses TCP 20,21!
- 2 TCP ports for 2 reasons:
- TCP 21 (Control Channel): to establish connection between
Server and Client
- TCP 20 (Data Channel): to transfer Data between
Server and Client |
| Trivial FTP (TFTP) ? | - uses UDP 69
- UDP so, unreliable, but still has it’s uses . |
