640-407 | Cisco Certified Network Associate

Errata for CCNA Study Guide by Todd Lammle, et. al.

The publisher of this book offers a limited errata. I highly recommend downloading this errata and making the necessary corrections. In addition, consider the changes suggested below.

Page 57:
Reads: Bridges will forward packets and multicast packets
Should Read: Bridges will forward broadcast and multicast packets

Page 103:
Reads: ...contains the hardware address of the source computer 100.100.100.1
Should Read: ...contains the hardware address of the source computer 00:a0:24:6e:of:a8

Page 106-107:

Text suggests that communication with a remote host will result in the arp cache contain entries only for the default gateway. In actuality the arp cache will likely contain entries for both the default gateway and the remote host. However, both entries will show the physical address of the default gateway. In Windows95/98, the result of the typing "arp -a" as presented in the book will actually return something more like the following:

    Interface: 100.100.100.2
      Internet Address      Physical Address      Type
      100.100.100.2         20-53-52-43-00-00     dynamic
      200.200.200.1         20-53-52-43-00-00     dynamic

Note here that the Internet Address for both the default gateway appears as well as the remote host. However, both physical addresses represent the default gateway.

Page 127:

Text suggests that the "default subnet mask" can not be shortened and that to do so would result in the host reading it as invalid and not letting you type even type it in. However, this is perfectly acceptable under some circumstances and is, in fact, the essence of "supernetting". While supernetting is perhaps a more advanced topic, this section should be reworded more carefully.

Page 128, 132-133:

This discussion of the use of the "special case" subnets appears inconsistent in regards to the use of the all-one's subnets. Page 128 recognizes the possible use of subnet 0 and continues with the modification of the formula to calculating the number of subnets as 2^n-1. Page 132 goes on, however, to describe the /28 subnet mask. Here the author points out the the 2^n-2 forumula clearly wouldn't apply then continues to describe a scenrio that clearly doesn't work with the 2^n-1 formula either since the author is not only use the all-zeros subnet but the all-ones as well. It is never explained why the all-ones subnet is being allowed. A link to a full discussion on the use of the all-ones subnet can be found my collection of additional Cisco IP notes.

Page 133:

Note at bottom of page indicates that the router could assume that a workstation is on a different subnet if the workstation has an incorrect subnet mask. In fact the router will have no knowledge of the specific subnet maks for any workstation as it is not included in any communication between the workstation and the router. The follow statement regarding the router not forwarding packets to such a host, therefore, makes no sense. The last sentence of the note further suggests that such a configured workstation will send packets to the default gateway when it shouldn't. This may or may not be true depending on the nature of the error. For instance, if the error is that the subnet mask is too short, the workstation will actually send packets to the router LESS OFTEN than it should. It will incorrectly interpret some remote traffic as local and therefore not forward the packets to the default gateway. A note regarding the effects of incorrectly configured subnet masks is well warrented, but this note is entirely wrong.

Page 160:

Three quarters of the way down the page, an example of the column shifting that occurs while entering a long line is displayed. However, as the second example is listed, after a shift, not only has the line shifted but it has also changed. Specifically, the access-list number changes from 110 to 111.

Page 193:

Table toward bottom of page has "Default Gateway" as the last column. This should read "Address/Interface".

Page 205:

Question 7, answer A, reads: Static Routers Should read: Static routes

Page 331:

Text mentions "Notice that each fram type in Figure 9.3 has a unique IPX network address." This is in reference to Figure 9.3. Unfortunately, Figure 9.3 does not list the IPX network addresses.

Page 365:

This isn't really a technical innacuracy, just something that could be clarified. The section on access lists shows an access list that allows selected access to a specific destination using port 8080, a proxy port. It also allows any web traffic. The section continues to describe using a "browser" to reload a web page. Next the access list is shown again, this time relfecting a change in the number of matches to one of the entries filtering on port 8080. To many it may be obivous as to why this happens, but it many be beneficial to explain that the web browser has been configured to request pages through a proxy, which is whay the proxy filter is increasing and not the web filter. Finally, it is mentioned that the increase in matches is greater than 1 due to the web page having multiple objects. This is true, but is is more precisely due to the request requring multiple packets. This distinction is significant because depending on the type and direction of the access list, it is conceivable that a single LARGE object would require multiple packets and the counter would reflect this, despite there being only one object.

Page 412:

TE1 and TE2 are described as "Terminal Equipment" while on page 414 they are described as "Terminal End Points". The terminology should be kept consistent. It is also mentioned here that TE2s predate ISDN standards. This isn't entirely true, TE2s simply don't have built in ISDN capablity.

I hope this errata helps those using this book to study. Some of the points here being made are nit-picky, but better to be thorough. Don't let the occurance of errors in a book disuade you from reading the book. Simply be aware of them while you read. Errors in techincal books are common, partly due to the deadlines placed on authors by publishers in their effor to be the first to market with a book. Other reasons include the publishers quality control mechanisms and technical review procedures.