OAM functions and mechanisms for Ethernet based networks

OAM Functions:Error Reporting, Configuration, Management(ICMP, DHCP, NAT, SNMP) and ethernet connectivity fault management
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Dr.ShivJindal,India,Teacher
Published Date:19-07-2017
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OAM Functions: Error Reporting, Configuration, Management (ICMP, DHCP, NAT, SNMP) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Operations and Management (OAM)  Error Reporting (ICMP); Tools: ping, traceroute  Configuration: RARP, BOOTP, DHCP  Address Management: DHCP, Private Addresses, NAT, RSIP  Network Management: SNMP, RMON  Ref: Chap 5,6,9,20,23,30: Doug Comer textbook, Interconnections by Perlman  Reference Site: IETF NAT Working Group  Reference: RFC 2663: IP Network Address Translator (NAT) Terminology and Considerations: In HTML  Reading: RFC 3022: Traditional IP Network Address Translator (Traditional NAT):  Reference: Borella et al, RFC 3102: Realm Specific IP: Framework, In HTML Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2ICMP Features  Used by IP to send error and control messages  Uses IP to send its messages  Does not report errors on ICMP messages.  ICMP message are not required on datagram checksum errors.  ICMP reports error only on the first fragment ICMP Header ICMP Data IP Header IP Data Datalink Header Datalink Data Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3ICMP Message Format IP Header 8b Type of Message 8b Error Code 16b Checksum Var Parameters, if any Var Information  ICMP error messages normally include the IP header of the datagram that generated the error, plus at least 8 bytes following the IP header = Typical ICMP message sizes = 70 bytes Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Sample ICMP Messages  Echo Request/Reply: Used in ping  Source Quench: Please slow down I just dropped one of your datagrams.  Congestion control function: deprecated…  Time Exceeded: Time to live field in one of your packets became zero.” or “Reassembly timer expired at the destination.  Fragmentation Required: Datagram was longer than MTU and “No Fragment bit” was set.  Used in fragmentation/reassembly and path MTU detection Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Sample ICMP Messages (Continued)  Address Mask Request/Reply: What is the subnet mask on this net? Replied by “Address mask agent”  Redirect: Send to router X instead of me. Configuration functions… Redirect used. Mask config handled by BOOTP/DHCP.  Time Stamp Request/Reply: used to find current time or RTT. Deprecated… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6ICMP: Message Types Summary Type Message 0 Echo reply 3 Destination unreachable 4 Source quench 5 Redirect 8 Echo request 11 Time exceeded 12 Parameter unintelligible 13 Time-stamp request 14 Time-stamp reply 15 Information request 16 Information reply 17 Address mask request 18 Address mask reply Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7ICMP-based tools: Ping  Ping: Used to test destination reachability, compute round trip time count the of hops to destination may provide record route option.  Ping failure does not guarantee unreachability. Firewalls may filter pings. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8ICMP-based tools: Traceroute  Traceroute: Exploit TTL and ICMP Send the packet with time-to-live = 1 (hop) The first router discards the packet and sends an ICMP “time-to-live exceeded message” Send the packet with time-to-live = 2 (hops) etc… Does not use optional features like record route Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9ICMP-based tools: Path MTU Discovery  Send a large IP datagram with “Don’t fragment” bit set. Failure to fragment at a link will result in ICMP message. Later version of ICMP specifies MTU size in such ICMP messages.  Reduce MSS until success (No ICMP message received) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10Configuration: Issues  Configuration: give protocols the parameters they need to operate  Several things to configure… Eg scenario: Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 117 Things to configure…  1. End systems need Layer 3 address, names, masks  2. Router finds Layer 3 addresses of end systems  3. Router finds Layer 2 addresses of end systems  4. End systems find a (default) router, name server  5. End nodes on the same LAN discover that they can send directly to each other  6. End systems find the best router for exit traffic  7. End systems communicate on a router-less LAN  Typically end systems only know their hardware (IEEE 802) address… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Method 1: Reverse ARP (RARP)  H/w (MAC) address - IP address mapping  End system broadcasts RARP request…  RARP server responds.  Once IP address is obtained, use “tftp” to get a boot image. Extra transaction  RARP design complex:  RARP server is a user process and maintains table for multiple hosts (/etc/ethers). Contrast: no ARP server  RARP needs a unique Ethernet frame type (0x8035) & works through a special kernel-level filter  Multiple RARP servers needed for reliability RARP servers cannot be consolidated since RARP requests are broadcast = router cannot forward  After all this, you get only the L3 (IP) address Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Method 2: BOOTP  Runs over UDP/IP as a user process IP software can broadcast (to 255.255.255.255) even if local IP address unknown = client broadcasts BOOTP request Port number 67 for server and 68 for client (not an ephemeral port) Delivers BOOTP reply to BOOTP client and not other UDP apps when reply is broadcast Does not wake up other servers during broadcast reply Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14BOOTP (Continued) BOOTP requests/replies sent w/ DF bit set.  Server can send reply via broadcast or unicast: For unicast reply, BOOTP server knows the IP address, but the link layer address is not in the ARP cache Note that the server cannot send an ARP message because client does not know its IP address Server can use ioctl(8) or arp -s to set the value of the cache based upon BOOTP request = can do this only if it has permission Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15BOOTP Features (Continued) Else send broadcast reply  Reply: IP Address, Boot Server IP address, Default Router, Boot file name, subnet mask More information, but still only a single packet exchange Client gets boot image using TFTP = booting still a 2-step process Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16BOOTP features (Continued)  Advantages of using UDP/IP:  Bootstrapping can occur across a router via a relaying mechanism  BOOTP uses checksum provided by UDP  Multiple requests/replies  Process the first one  Client uses a transaction ID field to sort out replies  Clients responsible for reliability  Uses timeout, retransmission & exponential backoff  Random initial timeout (betn 0 & 4s): simultaneous reboot after power restoration. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17BOOTP Message Format 0 31b Operation H/W Type H/W Length Hops Transaction Identifier Seconds elapsed Unused Client IP Address Your IP Address Server IP Address Router IP Address Client H/W address 16 B Server Host Name 64 B 128 Bootfile Name B 64 Vendor Specific Area Shivkumar Kalyanaraman Rensselaer Polytechnic Institute B 18BOOTP Message (Continued)  Operation: 1 = Request, 2 = Reply  H/w type: 1 = Ethernet  H/w Address Length  Hops: Initialized to zero. Incremented by BOOTP relays (routers) BOOTP BOOTP BOOTP Please tell me My client needs Client Relay Server my address an address Your address is ... Your client’s address is ... Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19BOOTP Message  Boot File name: Generic name like "unix" in the request. Full name in response.  Vendor specific area: Misnomer. Also used for general purpose info. Magic cookie: First 4 octets = 99.130.83.99 Type-length-value: describes the option Item Code Length Padding 0 - Subnet mask 1 4 Time of Day 2 4 End 255 - Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20