Answers to the Chapter 5 Q&A Section 741
47
How many subnets could be created if using static length masks in a Class B network when
the mask is 255.255.255.224? What about when the mask is 255.255.252.0?
With a Class B network, the first 16 bits are network bits. With mask 255.255.255.224,
there are 5 host bits, leaving 11 subnet bits. 2
11
is 2048. If the zero and broadcast subnets
are avoided, 2046 are left. For the mask 255.255.252.0, there are 10 host bits, leaving 6
subnet bits. 2
6
is 64; if avoiding the two special cases, that leaves 62 possible subnets.
48
How many bytes comprise an IPX address?
Ten bytes. The network portion is 32 bits, and the node portion is 48 bits. The node part
conveniently is the same size as a LAN MAC address.
49
What do IPX and SPX stand for?
Internetwork Packet Exchange and Sequenced Packet Exchange.
50
Define encapsulation in the context of Cisco routers and Novell IPX.
Data link encapsulation describes the details of the data link header and trailer created by
a router as the result of routing a packet out an interface. Novell allows several options on
LANs. Encapsulation is used for any routed protocol on every router interface. Novell just
happens to have many options that are still in use, particularly on Ethernet.
51
Give an example of an IPX network mask used when subnetting.
There is no such thing as subnetting with IPX. This is an example of a question meant to
shake your confidence on the exam. Thoughts like, "I never read about subnetting IPX!"
can destroy your concentration. Be prepared for unusual questions or answers like this on
the exam.
52
Describe the headers used for two types of Ethernet encapsulation when using IPX.
Ethernet_II uses Ethernet version 2 headers (destination and source address, and
type field). Ethernet_802.3 uses an 802.3 header (destination and source address, and
length field). Ethernet_802.2 uses an 802.3 header and an 802.2 header (802.2 adds DSAP,
SSAP, and Control fields). Ethernet_SNAP uses an 802.3 header, an 802.2 header, and
then a SNAP header (SNAP adds OUI and protocol fields). The names in this answer use
Novell's names. The corresponding keywords in the IOS are arpa, novell-ether, SAP, and
SNAP, respectively. The Novell names refer to the last header before the IPX header. See
Table 5-32 and Table 5-33, on pages 301 and 302, for a reference for all LAN
encapsulations.
53
Name the part of the NetWare protocol specifications that, like TCP, provides end-to-end
guaranteed delivery of data.
SPX (Sequenced Packet Exchange).
apA.fm Page 741 Monday, March 20, 2000 5:24 PM