hdlc 抓包分析

港控/mmm° 2022-01-12 14:51 373阅读 0赞

# HDLC 包分析
    Frame 17: 24 bytes on wire (192 bits), 24 bytes captured (192 bits) on interface 0
    Cisco HDLC
        Address: Multicast (0x8f)           # 地址：0x8f为组播，0x0f为单播
        Control: 0x00                       # 控制：通常设置为0x00
        Protocol: SLARP (0x8035)            # 协议：0x8035 为SLARP，0x0800为IP
    Cisco SLARP
        Packet type: Line keepalive (2)     # 0x02 为keep-alives包
        Outgoing sequence number: 12        # 已发送keep-alives包的序号，每发送一个包，加1
        Returned sequence number: 0         # 上一次接受到keep-alives包的序号
        Reliability: 0xffff

# HDLC每隔10秒钟就互相发送链路探测的协商报文(KeepAlive报文)，用于探查链路是否中断，
    # 每次收发的报文按序号递增，序号失序则链路中断。
    # 当接口连续3次(数据包速率超过1000packets/s时为6次)没有收到对方对自己的递增序号的确认时，
    # HDLC协议就把链路状态由Up转变为Down，链路将不可用。
    5 10.422351 N/A N/A SLARP 24 Line keepalive, outgoing sequence 1, returned sequence 0
    6 20.428553 N/A N/A SLARP 24 Line keepalive, outgoing sequence 2, returned sequence 0
    7 30.439159 N/A N/A SLARP 24 Line keepalive, outgoing sequence 3, returned sequence 0
    
    # 连续3次没收到确认，两路状态由Up转变为Down
    R2(config-if)#
    *Aug 22 15:22:21.393: %LINK-3-UPDOWN: Interface Serial2/2, changed state to up
    *Aug 22 15:22:22.403: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/2, changed state to up
    R2(config-if)#end
    R2#
    *Aug 22 15:22:49.957: %SYS-5-CONFIG_I: Configured from console by console
    *Aug 22 15:22:50.842: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/2, changed state to down  
    R2#wr
    Building configuration...
    [OK]
    R2#sh int s2/2
    Serial2/2 is up, line protocol is down 
      Hardware is M4T
      Internet address is 202.100.23.2/24
      MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec, 
         reliability 255/255, txload 1/255, rxload 1/255
      Encapsulation HDLC, crc 16, loopback not set      # 默认封装协议为HDLC
      Keepalive set (10 sec)                            # HDLC keepalive时间 默认为10s
      Restart-Delay is 0 secs
      Last input never, output 00:00:06, output hang never
      Last clearing of "show interface" counters never
      Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
      Queueing strategy: fifo
      Output queue: 0/40 (size/max)
      5 minute input rate 0 bits/sec, 0 packets/sec
      5 minute output rate 0 bits/sec, 0 packets/sec
         0 packets input, 0 bytes, 0 no buffer
         Received 0 broadcasts (0 IP multicasts)
         0 runts, 0 giants, 0 throttles 
         0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
         12 packets output, 1275 bytes, 0 underruns
         0 output errors, 0 collisions, 2 interface resets
         0 unknown protocol drops
         0 output buffer failures, 0 output buffers swapped out
         3 carrier transitions     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up
    # DCD=up DSR=up DTR=up RTS=up CTS=up 只有链路第一层正常工作时，均为up，则keepalive机制生效。
    # 如果 DCD=up DSR=up DTR=up RTS=up CTS=up这些项中有一项未激活，keepalive就不会工作。
    
    # 收到keep-alive后，将返回收到的keep-alives 序号，
    21 130.235657 N/A N/A SLARP 24 Line keepalive, outgoing sequence 1, returned sequence 0    # 发送序号为 1，接受序号为 0
    22 130.511801 N/A N/A SLARP 24 Line keepalive, outgoing sequence 13, returned sequence 1   # 发送序号为 13，接受序号为 1
    
    25 140.249595 N/A N/A SLARP 24 Line keepalive, outgoing sequence 2, returned sequence 13    
    26 140.515803 N/A N/A SLARP 24 Line keepalive, outgoing sequence 14, returned sequence 2

# 202.100.23.2 ping 202.100.23.3 HDLC过程分析
    R2#ping 202.100.23.3
    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 202.100.23.3, timeout is 2 seconds:
    !!!!!
    
    # 1、查路由表，存在路由，则转发；否则，丢弃
    R2#sh ip route 202.100.23.3
    Routing entry for 202.100.23.0/24
      Known via "connected", distance 0, metric 0 (connected, via interface)
      Routing Descriptor Blocks:
      * directly connected, via Serial2/2
          Route metric is 0, traffic share count is 1、
    
    # 2、封装
    # 三层封装：ICMP request请求 source ip address 为出接口地址为源地址(路由表决定); destination ip address: 202.100.23.3 
    Frame 49: 104 bytes on wire (832 bits), 104 bytes captured (832 bits) on interface 0
    Cisco HDLC
        Address: Unicast (0x0f)    # 地址：0x0f为单播
        Control: 0x00
        Protocol: IP (0x0800)      # 协议：0x0800 为IP协议
    Internet Protocol Version 4, Src: 202.100.23.2, Dst: 202.100.23.3    # 目的地址为 ping 地址
        0100 .... = Version: 4
        .... 0101 = Header Length: 20 bytes (5)
        Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        Total Length: 100
        Identification: 0x0000 (0)
        Flags: 0x00
        Fragment offset: 0
        Time to live: 255
        Protocol: ICMP (1)
        Header checksum: 0xf8ca [validation disabled]
        [Header checksum status: Unverified]
        Source: 202.100.23.2
        Destination: 202.100.23.3
        [Source GeoIP: Unknown]
        [Destination GeoIP: Unknown]
    Internet Control Message Protocol
        Type: 8 (Echo (ping) request)
        Code: 0
        Checksum: 0xb3a7 [correct]
        [Checksum Status: Good]
        Identifier (BE): 0 (0x0000)
        Identifier (LE): 0 (0x0000)
        Sequence number (BE): 0 (0x0000)
        Sequence number (LE): 0 (0x0000)
        [Response frame: 50]
        Data (72 bytes)
        
    Frame 50: 104 bytes on wire (832 bits), 104 bytes captured (832 bits) on interface 0
    Cisco HDLC
        Address: Unicast (0x0f)
        Control: 0x00
        Protocol: IP (0x0800)
    Internet Protocol Version 4, Src: 202.100.23.3, Dst: 202.100.23.2
        0100 .... = Version: 4
        .... 0101 = Header Length: 20 bytes (5)
        Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        Total Length: 100
        Identification: 0x0000 (0)
        Flags: 0x00
        Fragment offset: 0
        Time to live: 255
        Protocol: ICMP (1)
        Header checksum: 0xf8ca [validation disabled]
        [Header checksum status: Unverified]
        Source: 202.100.23.3
        Destination: 202.100.23.2
        [Source GeoIP: Unknown]
        [Destination GeoIP: Unknown]
    Internet Control Message Protocol
        Type: 0 (Echo (ping) reply)
        Code: 0
        Checksum: 0xbba7 [correct]
        [Checksum Status: Good]
        Identifier (BE): 0 (0x0000)
        Identifier (LE): 0 (0x0000)
        Sequence number (BE): 0 (0x0000)
        Sequence number (LE): 0 (0x0000)
        [Request frame: 49]
        [Response time: 13.349 ms]
        Data (72 bytes)
        
    # HDLC缺点：没有认证功能，接口互连即可使用；点对点协议，不支持点到多点；

转载于:https://blog.51cto.com/f1yinsky/1958212