The difference between Tcp and udp protocols
How to ensure the reliability of TCP:
In the TCP protocol for reliable data transmission to make a guarantee, shaking hands with the need to disconnect the two sides confirmed communication, data transmission also requires both sides to confirm the success of the agreement also provides for: subcontracting, restructuring, retransmission and other rules; and UDP mainly for unreliable connection, we can not guarantee that the data reach the correct destination.
Three-way handshake:
In the TCP / IP protocol, TCP protocol provides reliable connectivity services, three-way handshake to establish a connection.
The first handshake: connection is established, the client sends syn packets to the server, and enter SYN_SEND state, waiting for the server to confirm;
second handshake: server receives syn packets, must confirm the customer's SYN, while he is sending a SYN packet , i.e. SYN + ACK packet, then the server enters a state SYN_RECV;
third handshake: the client receives the SYN + ACK packet to the server, the server sends an acknowledgment to the ACK packet, this packet been sent, the client and server into the ESTABLISHED state, complete the three handshake.
Complete three-way handshake, the client and the server begins transmitting data.
Four break up:
(1) A client sends a FIN, for closing the client A to the server B transmits data (segment 4).
(2) Server B receives the FIN, it sends back an ACK, acknowledgment received sequence number plus 1 (segment 5). And SYN as a FIN will take a number.
(3) closes the server B is connected to the client A, the client sends a FIN A (segment 6).
(4) A client sends back ACK message ACK by incrementing the received sequence number by 1 (segment 7).
OSI seven-layer model
TCP / IP five layer model agreement
ARP protocol in the OSI model link layer belongs; in TCP / IP model, ARP protocol belongs to network layer.
OSI model and the TCP / IP protocol What is the difference
ARP protocol works
1, each host will establish an ARP list, to indicate a correspondence between the IP address and MAC address.
2, will send ARP packets to broadcast their own mapping between IP address and Mac address of the host to a host of other new entrants to the network.
3, the host on the network upon receiving the ARP packet will update their ARP list. The new mapping relationship to update its ARP table.
4, when a host needs to send packets, first checks whether the IP address corresponding to the object of the ARP list of MAC addresses, if any, data is transmitted directly, if not, sends the data to all hosts ARP network segment packet, the packet contents includes: IP address of the source host, the source host MAC address, an IP address of the destination host.
5, when all the hosts of this network received the ARP packet:
(A) First, check whether the IP address of the packet is its own IP address, and if not, the packet is ignored.
(B) If so, the first removed from the packet source host the MAC address written in the IP and ARP list, if it already exists, it is overwritten.
(C) and then write its own MAC address ARP response packet, the source host to tell myself that it is the MAC address you want to find.
6. After the source host receives the ARP response packet. The destination host IP and MAC address is written ARP list, and use this information to transmit data. If the source host has not received ARP response packet, it represents an ARP query failed.
Domain name resolution process
What, what principles routing protocols,
Including the RIP, the OSPF, the BGP
the RIP
"Routing Information Protocol (Route Information Protocol)" in abbreviation, the main transfer routing information, broadcast every 30 seconds by a routing table, maintaining the positional relationship between the adjacent router, while the routing table according to the received information to calculate its own routing table information. RIP is a distance vector routing protocol, the maximum hop count of 15 jumps, jumping more than 15 network destination is considered unreachable network.
The OSPF
the OSPF protocol is the "Open Shortest Path First (Open Shortest Path First)" in abbreviation, belonging to link state routing protocol. OSPF put forward the concept of "region (area)", and all the routers in each region maintains an identical link state database (LSDB). Backbone area is divided into regions, if a running OSPF network there is only a single area, the backbone area or region may be non-backbone area. If there are multiple areas of the network, then there must be the backbone area and non-backbone areas must be directly connected to the backbone area. Using OSPF link-state database maintained by Shortest Path First (SPF algorithm) calculated by the routing table.
BGP
order to safeguard the interests of the various independent ISP, standardization organizations to develop a routing protocol BGP between the ISP. BGP is the "Border Gateway Protocol (Border Gateway Protocol)" in abbreviation, the processing route transfer between the ISP.
There are several OSPF protocol packets that? Their role?
1.Hello package for establishing and maintaining neighbor relationships, send each other once every 10s, over 40s is not sent, then delete the neighbor relationship
2.DBD packet (database description), database description packets to describe their routes to other ospf network topology
3.LSR packet (link status request), for requesting other routing information
4.LSU packet (ling status update), for transmitting stored, update the routing information
5.LSACK (link status acknowledge), to LSU confirmation packet
OSPF neighbors formation process?
Send each HELLO packet, forming a bidirectional communication
according to the network type selected from the DR / BDR
send a first DBD, selected from the master
for DBD synchronized
for synchronous interaction LSA LSR, LSU, LSack
after the end of the synchronization enter FULL
There are several types of OSPF LSA? Who generated?
A class of all routers in the router LSA Direct topology information region describes
two types of network LSA describes the DR region and the neighboring network segment mask
three aggregated network routing information related to the ABR region between the LSA area
four relevant area the ABR ASBR Summary LSA a routing information destined for the ASBR
external entire LSA ASBR AS AS external routes five
seven types of the present NSSA external LSA NSSA area AS external routing information ASBR
OSPF packet carried in a complete link status?
LSU
Comparison of link-state protocols and distance-vector protocols?
(1) routing of different delivery methods (2) different speeds convergence (3) of different magnitudes (4) acyclic ring
(5) different applications (6) with or without hops limit (7) to generate different routing algorithm (8) different consumption of device resources
OSPF anti-ring measures?
(1) SFP algorithm acyclic (2) update the information carrying originator information and first-hand information requirements for the non-backbone area (3) multi-zone, must be connected to the backbone area, in order to exchange routing, preventing originator information loss, to avoid the loop.
OSPF is a link-state protocol pure do?
Single area is pure link-state protocol, and multi-regional, inter-regional routes use distance vector algorithms.
? Significance in OSPF DR election
? Network type when DR election
relations DR and other routers?
(1) improve the efficiency of LSA synchronization. (2) to be broadcast and NBMA selected from the group DR (3) DR abutting relationship with the other router.
The difference between OSPF NSSA area and other areas?
Compared than the average area: In addition to the four categories of ASBR summary LSA, five external LSA, an increase of seven types of external LSA NSSA
and STUB area compared: one way he can import external routes
Why employ a full-mesh IBGP? Without full Internet how to deploy?
(1) the level of segmentation problem solving IBGP (2) reflector or confederation
Reflection principle RR?
Route reflectors (1) the client to all neighbors (2) the route reflector non-client to the client (3) only send the optimal route (4) two non-route the client can not communicate (5) reflection is not changed route attributes
The reason FULL state OSPF does not form?
(1) HELLO and expiration time inconsistency
(2) is inconsistent network interfaces
(3) inconsistent region
(4) MA inconsistent network mask
(5) inconsistent versions
(6) authentication fails
(7) the same ID-SPEED ROUTER
(. 8) MA network priority are 0
(. 9) not match the MTU
(10) is not the same numerals special area
(11) underlying barrier
(12) NBMA network not refer to neighbor
OSPF virtual link used under what circumstances?
Why use virtual link?
(1) the discontinuous areas or areas will be used is divided into 0
(2) because all areas must be attached to the area 0, 0 when the region is divided, the divided two regions of routes 0 can not be exchanged.
The role of OSPF virtual link? Why backbone area?
Because all regions must be attached to the area 0, 0 when the region is divided, the divided two regions of routes 0 can not be exchanged.
Backbone region is provided for preventing routing loops multi-regional area
RIP routing protocol loop problem-solving mechanisms?
(1) horizontal split (2) Maximum hops 16 (3) routing poison (4) toxicity reversal (5) inhibition timer (6) triggered updates
PPP negotiation process?
(1) detects the carrier enters the link establishment phase (2) LCP negotiation (3) authentication (4) NCP (IPCP) negotiation