Network Management

Summer 2016, Corboy 710, TTh 5:30-8:45 pm

Class 3: July 12

Notes on the iReasoning tool and snmpd

Most of you had no trouble installing the iReasoning MIB browser.

Getting snmpd configured and working is usually more complicated.

Review tables

Fundamental SNMP-v1 messages:

SET
GET
GET-NEXT
response to above
TRAP

atomic data values only! Note use of GET-NEXT to retrieve these.

Issues:
   data presentation (eg byte order, but much more)
   NAMING for all those possible attributes!

ASN.1/BER data representation: defer

data can be subdivided into fields, though it is not for SNMP.

ASN.1

AICN 20.6

See also http://luca.ntop.org/Teaching/Appunti/asn1.html.

SNMP uses Abstract Syntax Notation 1 (ASN.1) to define syntax; encoding into UDP packets is then done using the Basic Encoding Rules (BER). Right now it sufficies to note the following:

BER data is tagged with its type.
ASN.1 and BER supports compound data types. However, SNMP does not use these; all data is atomic. (However, SNMP does support tables, which corresponds roughly to record formats and which can be pressed into service to represent, say, arrays.)
SNMP uses the ASN.1 type constructors SEQUENCE (to define lists) and SEQUENCE OF (to define records). A table is a SEQUENCE of records; each record is a SEQUENCE OF a specific list of fields. (ASN.1 also has SET and SET OF constructors, but SNMP does not use these directly.)
ASN.1 also supports CHOICE types, but these are used in SNMP only for very high-level definitions, eg
                  SimpleSyntax ::=
                      CHOICE {
                          number
                              INTEGER,
                          string
                              OCTET STRING,
                          object
                              OBJECT IDENTIFIER,
                          empty
                              NULL
                      }
SNMP does not use all the available basic ASN.1/BER data types. In fact, only INTEGER, OCTET STRING, OBJECT IDENTIFIER, and NULL are allowed. However, some subtypes of INTEGER are created; these are called defined types. See intronetworks.cs.luc.edu/current/html/netmgmt.html#snmpv1-data-types.
The BER encoding is such that the actual size in bytes of the data can be difficult to predict.

Some defined types from RFC 1155 (AICN 20.5)

IpAddress: (a 4-byte OCTET STRING in network byte order)
Counter: (a non-negative INTEGER which increases monotonically to 2^32-1 until it wraps around)
Gauge: a nonnegative integer which "latches at a maximum value". This generally means that if it ever hits the maximum, it sticks there and will not decrease. Thus, if it hits the maximum, you will know.
TimeTicks: an INTEGER representing time measured in 10ms (0.01 sec) units.
Opaque: an arbitrary byte string, encoded as an OCTET STRING.

ASN.1 has more built-in data types. Every type is either Universal, Application-specific, Private, or Context-specific. Some of the universal types are BITSTRING, UTCTime, and PrintableString.

Some ASN.1:

Some definitions of high-level OID prefixes:

      internet    OBJECT IDENTIFIER ::= { iso org(3) dod(6) 1 }


      directory     OBJECT IDENTIFIER ::= { internet 1 }
      mgmt          OBJECT IDENTIFIER ::= { internet 2 }
      experimental  OBJECT IDENTIFIER ::= { internet 3 }
      private       OBJECT IDENTIFIER ::= { internet 4 }

For defining records (eg ifEntry, or other table rows):

      SEQUENCE { <type1>, ..., <typeN> }

Tables are lists of records, defined with

      SEQUENCE OF <entry>

The OBJECT-TYPE macro is ubiquitous in MIB files. It provides a uniform way to specify the value's type (the SYNTAX) field, and also the ACESS and STATUS fields. The notation closes with "::= <OIDvalue>".

      OBJECT-TYPE MACRO ::=
      BEGIN
          TYPE NOTATION ::= "SYNTAX" type (TYPE ObjectSyntax)
                            "ACCESS" Access
                            "STATUS" Status
          VALUE NOTATION ::= value (VALUE ObjectName)

          Access ::= "read-only"
                          | "read-write"
                          | "write-only"
                          | "not-accessible"
          Status ::= "mandatory"
                          | "optional"
                          | "obsolete"
      END

Here are five examples of OBJECT-TYPE in use to define the (now-deprecated) at table (for ARP data). The OID for the at group is 1.3.6.1.2.1.3. It defines atTable as at.1 (that is, 1.3.6.1.2.1.3.1), and atEntry as atTable.1, and the three columns as atEntry.1, atEntry.2, and atEntry.3.

1.                atIndex OBJECT-TYPE
                         SYNTAX INTEGER
                          ACCESS read-write
                          STATUS mandatory
                          ::= { atEntry 1 }

2.                atPhysAddress OBJECT-TYPE
                          SYNTAX OCTET STRING
                          ACCESS read-write
                          STATUS mandatory
                          ::= { atEntry 2 }

3.                atNetAddress OBJECT-TYPE
                          SYNTAX NetworkAddress
                          ACCESS read-write
                          STATUS mandatory
                          ::= { atEntry 3 }

4.                atEntry OBJECT-TYPE
                          SYNTAX AtEntry
                          ACCESS read-write
                          STATUS mandatory
                          ::= { atTable 1 }

5.                atTable OBJECT-TYPE
                          SYNTAX SEQUENCE OF AtEntry
                          ACCESS read-write
                          STATUS mandatory
                          ::= { at 1 }

The first three entries define columns ("fields") of atEntry. The fourth defines atEntry as having OID atTable.1, and with syntax the CAPITALIZED AtEntry. The fifth defines atTable as having OID at.1, and with syntax SEQUENCE OF AtEntry.

Finally there is
                  AtEntry ::= SEQUENCE {
                      atIndex
                          INTEGER,
                      atPhysAddress
                          OCTET STRING,
                      atNetAddress
                          NetworkAddress
                  }
Every table has a row specification like this, with name capitalized by convention. Note that the OBJECT-TYPE is not used here. We could splice AtEntry into the fourth and fifth OBJECT-TYPE entries above, but it's simpler not to.

20.8: SNMP Operations

Get and GetNext
Multi-attribute Get
Set

VarBind Lists
Walking the OID tree

20.9: MIB Browsing
20.10: MIB-2

Software-Defined Networking

Mininet and Pox

Look at snmpd.conf on ulam3

Network Implementation Design Analysis � Burke, 2004, p 45

Geographical Distribution

Office
1. Subnets
2. LAN
Department (many offices)
1. Subnets
2. LAN
Division (many departments)
1. LAN
2. WAN
Organization (many divisions)
1. Local LAN/WAN
2. National WAN
3. Global WAN

Subnets

How many
1. bridges/switches
2. routers
Ethernet
1. cabling
2. speed
3. IP addresses needed
4. DHCP
Wireless
1. number of wireless hubs
2. authentication

LAN

How many of them
Domain names
DNS configuration
IP address space
Subnets / how many, subnet masks
switched Ethernet v routers
Other LAN technologies

WAN

How sites connect
PSTN, X.25, SONET, ATM, Frame Relay, Carrier Ethernet, etc

Bandwidth requirements

Video needs
Audio needs
Data needs

Service Level Agreements

bandwidth constantly available
peak bandwidth
bandwidth available on demand
burst capacity

Security

firewall configuration
proxy servers
authentication issues
network intrusion detection
virus/malware monitoring

Apply it to:

a set of offices on 10 floors of one building
a multi-city company with web servers

Table 3.2 from Burke, Network Management, 2004: this describes some of the data we want:

Reliability:

transmission error rates
dropped packets
link failures

Faults

proactive prevention
detection
location
correction time
link v node

Availability: MTBF

Performance (response time)

processor total use
interrupts/sec
queue length
etc

Throughput

bytes per second we're actually achieving
guaranteed throughput via our Service Level Agreement

Data packet throughput
Voice ordered packet throughput
Video bandwidth, ...
Utilization

packets/sec
transactions/sec

Resource use

application software
network devices (switches, routers, etc)
services
disk storage
cpu

Policies

Redundancy

User support

Note that this table does NOT have any per-service entries!
Some software services:

Windows Server Active Directory authentication
Windows file sharing: file access time
Web server
database server
integrated web/database
DNS
DHCP